diff --git a/vendor/github.com/gregjones/httpcache/httpcache.go b/vendor/github.com/gregjones/httpcache/httpcache.go
new file mode 100644
index 0000000..b41a63d
--- /dev/null
+++ b/vendor/github.com/gregjones/httpcache/httpcache.go
@@ -0,0 +1,551 @@
+// Package httpcache provides a http.RoundTripper implementation that works as a
+// mostly RFC-compliant cache for http responses.
+//
+// It is only suitable for use as a 'private' cache (i.e. for a web-browser or an API-client
+// and not for a shared proxy).
+//
+package httpcache
+
+import (
+	"bufio"
+	"bytes"
+	"errors"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"net/http/httputil"
+	"strings"
+	"sync"
+	"time"
+)
+
+const (
+	stale = iota
+	fresh
+	transparent
+	// XFromCache is the header added to responses that are returned from the cache
+	XFromCache = "X-From-Cache"
+)
+
+// A Cache interface is used by the Transport to store and retrieve responses.
+type Cache interface {
+	// Get returns the []byte representation of a cached response and a bool
+	// set to true if the value isn't empty
+	Get(key string) (responseBytes []byte, ok bool)
+	// Set stores the []byte representation of a response against a key
+	Set(key string, responseBytes []byte)
+	// Delete removes the value associated with the key
+	Delete(key string)
+}
+
+// cacheKey returns the cache key for req.
+func cacheKey(req *http.Request) string {
+	if req.Method == http.MethodGet {
+		return req.URL.String()
+	} else {
+		return req.Method + " " + req.URL.String()
+	}
+}
+
+// CachedResponse returns the cached http.Response for req if present, and nil
+// otherwise.
+func CachedResponse(c Cache, req *http.Request) (resp *http.Response, err error) {
+	cachedVal, ok := c.Get(cacheKey(req))
+	if !ok {
+		return
+	}
+
+	b := bytes.NewBuffer(cachedVal)
+	return http.ReadResponse(bufio.NewReader(b), req)
+}
+
+// MemoryCache is an implemtation of Cache that stores responses in an in-memory map.
+type MemoryCache struct {
+	mu    sync.RWMutex
+	items map[string][]byte
+}
+
+// Get returns the []byte representation of the response and true if present, false if not
+func (c *MemoryCache) Get(key string) (resp []byte, ok bool) {
+	c.mu.RLock()
+	resp, ok = c.items[key]
+	c.mu.RUnlock()
+	return resp, ok
+}
+
+// Set saves response resp to the cache with key
+func (c *MemoryCache) Set(key string, resp []byte) {
+	c.mu.Lock()
+	c.items[key] = resp
+	c.mu.Unlock()
+}
+
+// Delete removes key from the cache
+func (c *MemoryCache) Delete(key string) {
+	c.mu.Lock()
+	delete(c.items, key)
+	c.mu.Unlock()
+}
+
+// NewMemoryCache returns a new Cache that will store items in an in-memory map
+func NewMemoryCache() *MemoryCache {
+	c := &MemoryCache{items: map[string][]byte{}}
+	return c
+}
+
+// Transport is an implementation of http.RoundTripper that will return values from a cache
+// where possible (avoiding a network request) and will additionally add validators (etag/if-modified-since)
+// to repeated requests allowing servers to return 304 / Not Modified
+type Transport struct {
+	// The RoundTripper interface actually used to make requests
+	// If nil, http.DefaultTransport is used
+	Transport http.RoundTripper
+	Cache     Cache
+	// If true, responses returned from the cache will be given an extra header, X-From-Cache
+	MarkCachedResponses bool
+}
+
+// NewTransport returns a new Transport with the
+// provided Cache implementation and MarkCachedResponses set to true
+func NewTransport(c Cache) *Transport {
+	return &Transport{Cache: c, MarkCachedResponses: true}
+}
+
+// Client returns an *http.Client that caches responses.
+func (t *Transport) Client() *http.Client {
+	return &http.Client{Transport: t}
+}
+
+// varyMatches will return false unless all of the cached values for the headers listed in Vary
+// match the new request
+func varyMatches(cachedResp *http.Response, req *http.Request) bool {
+	for _, header := range headerAllCommaSepValues(cachedResp.Header, "vary") {
+		header = http.CanonicalHeaderKey(header)
+		if header != "" && req.Header.Get(header) != cachedResp.Header.Get("X-Varied-"+header) {
+			return false
+		}
+	}
+	return true
+}
+
+// RoundTrip takes a Request and returns a Response
+//
+// If there is a fresh Response already in cache, then it will be returned without connecting to
+// the server.
+//
+// If there is a stale Response, then any validators it contains will be set on the new request
+// to give the server a chance to respond with NotModified. If this happens, then the cached Response
+// will be returned.
+func (t *Transport) RoundTrip(req *http.Request) (resp *http.Response, err error) {
+	cacheKey := cacheKey(req)
+	cacheable := (req.Method == "GET" || req.Method == "HEAD") && req.Header.Get("range") == ""
+	var cachedResp *http.Response
+	if cacheable {
+		cachedResp, err = CachedResponse(t.Cache, req)
+	} else {
+		// Need to invalidate an existing value
+		t.Cache.Delete(cacheKey)
+	}
+
+	transport := t.Transport
+	if transport == nil {
+		transport = http.DefaultTransport
+	}
+
+	if cacheable && cachedResp != nil && err == nil {
+		if t.MarkCachedResponses {
+			cachedResp.Header.Set(XFromCache, "1")
+		}
+
+		if varyMatches(cachedResp, req) {
+			// Can only use cached value if the new request doesn't Vary significantly
+			freshness := getFreshness(cachedResp.Header, req.Header)
+			if freshness == fresh {
+				return cachedResp, nil
+			}
+
+			if freshness == stale {
+				var req2 *http.Request
+				// Add validators if caller hasn't already done so
+				etag := cachedResp.Header.Get("etag")
+				if etag != "" && req.Header.Get("etag") == "" {
+					req2 = cloneRequest(req)
+					req2.Header.Set("if-none-match", etag)
+				}
+				lastModified := cachedResp.Header.Get("last-modified")
+				if lastModified != "" && req.Header.Get("last-modified") == "" {
+					if req2 == nil {
+						req2 = cloneRequest(req)
+					}
+					req2.Header.Set("if-modified-since", lastModified)
+				}
+				if req2 != nil {
+					req = req2
+				}
+			}
+		}
+
+		resp, err = transport.RoundTrip(req)
+		if err == nil && req.Method == "GET" && resp.StatusCode == http.StatusNotModified {
+			// Replace the 304 response with the one from cache, but update with some new headers
+			endToEndHeaders := getEndToEndHeaders(resp.Header)
+			for _, header := range endToEndHeaders {
+				cachedResp.Header[header] = resp.Header[header]
+			}
+			resp = cachedResp
+		} else if (err != nil || (cachedResp != nil && resp.StatusCode >= 500)) &&
+			req.Method == "GET" && canStaleOnError(cachedResp.Header, req.Header) {
+			// In case of transport failure and stale-if-error activated, returns cached content
+			// when available
+			return cachedResp, nil
+		} else {
+			if err != nil || resp.StatusCode != http.StatusOK {
+				t.Cache.Delete(cacheKey)
+			}
+			if err != nil {
+				return nil, err
+			}
+		}
+	} else {
+		reqCacheControl := parseCacheControl(req.Header)
+		if _, ok := reqCacheControl["only-if-cached"]; ok {
+			resp = newGatewayTimeoutResponse(req)
+		} else {
+			resp, err = transport.RoundTrip(req)
+			if err != nil {
+				return nil, err
+			}
+		}
+	}
+
+	if cacheable && canStore(parseCacheControl(req.Header), parseCacheControl(resp.Header)) {
+		for _, varyKey := range headerAllCommaSepValues(resp.Header, "vary") {
+			varyKey = http.CanonicalHeaderKey(varyKey)
+			fakeHeader := "X-Varied-" + varyKey
+			reqValue := req.Header.Get(varyKey)
+			if reqValue != "" {
+				resp.Header.Set(fakeHeader, reqValue)
+			}
+		}
+		switch req.Method {
+		case "GET":
+			// Delay caching until EOF is reached.
+			resp.Body = &cachingReadCloser{
+				R: resp.Body,
+				OnEOF: func(r io.Reader) {
+					resp := *resp
+					resp.Body = ioutil.NopCloser(r)
+					respBytes, err := httputil.DumpResponse(&resp, true)
+					if err == nil {
+						t.Cache.Set(cacheKey, respBytes)
+					}
+				},
+			}
+		default:
+			respBytes, err := httputil.DumpResponse(resp, true)
+			if err == nil {
+				t.Cache.Set(cacheKey, respBytes)
+			}
+		}
+	} else {
+		t.Cache.Delete(cacheKey)
+	}
+	return resp, nil
+}
+
+// ErrNoDateHeader indicates that the HTTP headers contained no Date header.
+var ErrNoDateHeader = errors.New("no Date header")
+
+// Date parses and returns the value of the Date header.
+func Date(respHeaders http.Header) (date time.Time, err error) {
+	dateHeader := respHeaders.Get("date")
+	if dateHeader == "" {
+		err = ErrNoDateHeader
+		return
+	}
+
+	return time.Parse(time.RFC1123, dateHeader)
+}
+
+type realClock struct{}
+
+func (c *realClock) since(d time.Time) time.Duration {
+	return time.Since(d)
+}
+
+type timer interface {
+	since(d time.Time) time.Duration
+}
+
+var clock timer = &realClock{}
+
+// getFreshness will return one of fresh/stale/transparent based on the cache-control
+// values of the request and the response
+//
+// fresh indicates the response can be returned
+// stale indicates that the response needs validating before it is returned
+// transparent indicates the response should not be used to fulfil the request
+//
+// Because this is only a private cache, 'public' and 'private' in cache-control aren't
+// signficant. Similarly, smax-age isn't used.
+func getFreshness(respHeaders, reqHeaders http.Header) (freshness int) {
+	respCacheControl := parseCacheControl(respHeaders)
+	reqCacheControl := parseCacheControl(reqHeaders)
+	if _, ok := reqCacheControl["no-cache"]; ok {
+		return transparent
+	}
+	if _, ok := respCacheControl["no-cache"]; ok {
+		return stale
+	}
+	if _, ok := reqCacheControl["only-if-cached"]; ok {
+		return fresh
+	}
+
+	date, err := Date(respHeaders)
+	if err != nil {
+		return stale
+	}
+	currentAge := clock.since(date)
+
+	var lifetime time.Duration
+	var zeroDuration time.Duration
+
+	// If a response includes both an Expires header and a max-age directive,
+	// the max-age directive overrides the Expires header, even if the Expires header is more restrictive.
+	if maxAge, ok := respCacheControl["max-age"]; ok {
+		lifetime, err = time.ParseDuration(maxAge + "s")
+		if err != nil {
+			lifetime = zeroDuration
+		}
+	} else {
+		expiresHeader := respHeaders.Get("Expires")
+		if expiresHeader != "" {
+			expires, err := time.Parse(time.RFC1123, expiresHeader)
+			if err != nil {
+				lifetime = zeroDuration
+			} else {
+				lifetime = expires.Sub(date)
+			}
+		}
+	}
+
+	if maxAge, ok := reqCacheControl["max-age"]; ok {
+		// the client is willing to accept a response whose age is no greater than the specified time in seconds
+		lifetime, err = time.ParseDuration(maxAge + "s")
+		if err != nil {
+			lifetime = zeroDuration
+		}
+	}
+	if minfresh, ok := reqCacheControl["min-fresh"]; ok {
+		//  the client wants a response that will still be fresh for at least the specified number of seconds.
+		minfreshDuration, err := time.ParseDuration(minfresh + "s")
+		if err == nil {
+			currentAge = time.Duration(currentAge + minfreshDuration)
+		}
+	}
+
+	if maxstale, ok := reqCacheControl["max-stale"]; ok {
+		// Indicates that the client is willing to accept a response that has exceeded its expiration time.
+		// If max-stale is assigned a value, then the client is willing to accept a response that has exceeded
+		// its expiration time by no more than the specified number of seconds.
+		// If no value is assigned to max-stale, then the client is willing to accept a stale response of any age.
+		//
+		// Responses served only because of a max-stale value are supposed to have a Warning header added to them,
+		// but that seems like a  hassle, and is it actually useful? If so, then there needs to be a different
+		// return-value available here.
+		if maxstale == "" {
+			return fresh
+		}
+		maxstaleDuration, err := time.ParseDuration(maxstale + "s")
+		if err == nil {
+			currentAge = time.Duration(currentAge - maxstaleDuration)
+		}
+	}
+
+	if lifetime > currentAge {
+		return fresh
+	}
+
+	return stale
+}
+
+// Returns true if either the request or the response includes the stale-if-error
+// cache control extension: https://tools.ietf.org/html/rfc5861
+func canStaleOnError(respHeaders, reqHeaders http.Header) bool {
+	respCacheControl := parseCacheControl(respHeaders)
+	reqCacheControl := parseCacheControl(reqHeaders)
+
+	var err error
+	lifetime := time.Duration(-1)
+
+	if staleMaxAge, ok := respCacheControl["stale-if-error"]; ok {
+		if staleMaxAge != "" {
+			lifetime, err = time.ParseDuration(staleMaxAge + "s")
+			if err != nil {
+				return false
+			}
+		} else {
+			return true
+		}
+	}
+	if staleMaxAge, ok := reqCacheControl["stale-if-error"]; ok {
+		if staleMaxAge != "" {
+			lifetime, err = time.ParseDuration(staleMaxAge + "s")
+			if err != nil {
+				return false
+			}
+		} else {
+			return true
+		}
+	}
+
+	if lifetime >= 0 {
+		date, err := Date(respHeaders)
+		if err != nil {
+			return false
+		}
+		currentAge := clock.since(date)
+		if lifetime > currentAge {
+			return true
+		}
+	}
+
+	return false
+}
+
+func getEndToEndHeaders(respHeaders http.Header) []string {
+	// These headers are always hop-by-hop
+	hopByHopHeaders := map[string]struct{}{
+		"Connection":          {},
+		"Keep-Alive":          {},
+		"Proxy-Authenticate":  {},
+		"Proxy-Authorization": {},
+		"Te":                  {},
+		"Trailers":            {},
+		"Transfer-Encoding":   {},
+		"Upgrade":             {},
+	}
+
+	for _, extra := range strings.Split(respHeaders.Get("connection"), ",") {
+		// any header listed in connection, if present, is also considered hop-by-hop
+		if strings.Trim(extra, " ") != "" {
+			hopByHopHeaders[http.CanonicalHeaderKey(extra)] = struct{}{}
+		}
+	}
+	endToEndHeaders := []string{}
+	for respHeader := range respHeaders {
+		if _, ok := hopByHopHeaders[respHeader]; !ok {
+			endToEndHeaders = append(endToEndHeaders, respHeader)
+		}
+	}
+	return endToEndHeaders
+}
+
+func canStore(reqCacheControl, respCacheControl cacheControl) (canStore bool) {
+	if _, ok := respCacheControl["no-store"]; ok {
+		return false
+	}
+	if _, ok := reqCacheControl["no-store"]; ok {
+		return false
+	}
+	return true
+}
+
+func newGatewayTimeoutResponse(req *http.Request) *http.Response {
+	var braw bytes.Buffer
+	braw.WriteString("HTTP/1.1 504 Gateway Timeout\r\n\r\n")
+	resp, err := http.ReadResponse(bufio.NewReader(&braw), req)
+	if err != nil {
+		panic(err)
+	}
+	return resp
+}
+
+// cloneRequest returns a clone of the provided *http.Request.
+// The clone is a shallow copy of the struct and its Header map.
+// (This function copyright goauth2 authors: https://code.google.com/p/goauth2)
+func cloneRequest(r *http.Request) *http.Request {
+	// shallow copy of the struct
+	r2 := new(http.Request)
+	*r2 = *r
+	// deep copy of the Header
+	r2.Header = make(http.Header)
+	for k, s := range r.Header {
+		r2.Header[k] = s
+	}
+	return r2
+}
+
+type cacheControl map[string]string
+
+func parseCacheControl(headers http.Header) cacheControl {
+	cc := cacheControl{}
+	ccHeader := headers.Get("Cache-Control")
+	for _, part := range strings.Split(ccHeader, ",") {
+		part = strings.Trim(part, " ")
+		if part == "" {
+			continue
+		}
+		if strings.ContainsRune(part, '=') {
+			keyval := strings.Split(part, "=")
+			cc[strings.Trim(keyval[0], " ")] = strings.Trim(keyval[1], ",")
+		} else {
+			cc[part] = ""
+		}
+	}
+	return cc
+}
+
+// headerAllCommaSepValues returns all comma-separated values (each
+// with whitespace trimmed) for header name in headers. According to
+// Section 4.2 of the HTTP/1.1 spec
+// (http://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html#sec4.2),
+// values from multiple occurrences of a header should be concatenated, if
+// the header's value is a comma-separated list.
+func headerAllCommaSepValues(headers http.Header, name string) []string {
+	var vals []string
+	for _, val := range headers[http.CanonicalHeaderKey(name)] {
+		fields := strings.Split(val, ",")
+		for i, f := range fields {
+			fields[i] = strings.TrimSpace(f)
+		}
+		vals = append(vals, fields...)
+	}
+	return vals
+}
+
+// cachingReadCloser is a wrapper around ReadCloser R that calls OnEOF
+// handler with a full copy of the content read from R when EOF is
+// reached.
+type cachingReadCloser struct {
+	// Underlying ReadCloser.
+	R io.ReadCloser
+	// OnEOF is called with a copy of the content of R when EOF is reached.
+	OnEOF func(io.Reader)
+
+	buf bytes.Buffer // buf stores a copy of the content of R.
+}
+
+// Read reads the next len(p) bytes from R or until R is drained. The
+// return value n is the number of bytes read. If R has no data to
+// return, err is io.EOF and OnEOF is called with a full copy of what
+// has been read so far.
+func (r *cachingReadCloser) Read(p []byte) (n int, err error) {
+	n, err = r.R.Read(p)
+	r.buf.Write(p[:n])
+	if err == io.EOF {
+		r.OnEOF(bytes.NewReader(r.buf.Bytes()))
+	}
+	return n, err
+}
+
+func (r *cachingReadCloser) Close() error {
+	return r.R.Close()
+}
+
+// NewMemoryCacheTransport returns a new Transport using the in-memory cache implementation
+func NewMemoryCacheTransport() *Transport {
+	c := NewMemoryCache()
+	t := NewTransport(c)
+	return t
+}