oauth2: add Foursquare's Endpoint

Change-Id: If23b45150ac52c96f126e7d8e2a15f586bc3ac1c
Reviewed-on: https://go-review.googlesource.com/32010
Reviewed-by: Brad Fitzpatrick <[email protected]>

Author: Gareth Paul Jones

foursquare/foursquare.go

@@ -0,0 +1,16 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package foursquare provides constants for using OAuth2 to access Foursquare.
+package foursquare // import "golang.org/x/oauth2/foursquare"
+
+import (
+	"golang.org/x/oauth2"
+)
+
+// Endpoint is Foursquare's OAuth 2.0 endpoint.
+var Endpoint = oauth2.Endpoint{
+	AuthURL:  "https://foursquare.com/oauth2/authorize",
+	TokenURL: "https://foursquare.com/oauth2/access_token",
+}