PullRequest model now contains all of necessary fields

- Initial integration test for pull requests (can't seem to do much
without the tree api)
- Added Observable unit tests for the rest of the pull request client

Octokit/Models/Response/GitReference.cs

@@ -1,8 +1,38 @@
-namespace Octokit
+using Octokit.Internal;
+
+namespace Octokit
 {
     public class GitReference
     {
+        /// <summary>
+        /// The URL associated with this reference.
+        /// </summary>
         public string Url { get; set; }
+
+        /// <summary>
+        /// The reference label.
+        /// </summary>
+        public string Label { get; set; }
+
+        /// <summary>
+        /// The reference identifier.
+        /// </summary>
+        public string Ref { get; set; }
+
+        /// <summary>
+        /// The sha value of the reference.
+        /// </summary>
         public string Sha { get; set; }
+
+        /// <summary>
+        /// The user associated with this reference.
+        /// </summary>
+        public User User { get; set; }
+
+        /// <summary>
+        /// The repository associated with this reference.
+        /// </summary>
+        [Parameter(Key = "repo")]
+        public Repository Repository { get; set; }
     }
 }