Stubbed out the API for pull requests.

Still missing pull request files, commit lists and merge checks.

Octokit/Models/Request/PullRequestRequest.cs

@@ -0,0 +1,20 @@
+using Octokit.Internal;
+
+namespace Octokit
+{
+    public class PullRequestRequest : RequestParameters
+    {
+        public PullRequestRequest()
+        {
+            State = ItemState.Open;
+        }
+
+        public ItemState State { get; set; }
+
+        [Parameter(Key = "head")]
+        public string Head { get; set; }
+
+        [Parameter(Key = "base")]
+        public string Base { get; set; }
+    }
+}