Implemented pull request merge functionality

Octokit/Models/Request/MergePullRequest.cs

@@ -0,0 +1,22 @@
+using System;
+
+namespace Octokit
+{
+    /// <summary>
+    /// Used to merge a pull request.
+    /// </summary>
+    public class MergePullRequest
+    {
+        public MergePullRequest(string message)
+        {
+            Ensure.ArgumentNotNull(message, "message");
+
+            Message = message;
+        }
+
+        /// <summary>
+        /// The message that will be used for the merge commit (optional)
+        /// </summary>
+        public string Message { get; private set; }
+    }
+}