Repository invitations changes (#1410)

* add invitations accept header

* create class RepositoryInvitation

* add repository invitations client

* add api urls for invitations

* [WIP]

* add methods to repository invitations client

* add invite method to repo collaborators client

need to add some new overload to post method in apiconnection

* some changes

* add observable client

* add dependings

* add missing observable client

* add missing xml params

* check client

* change repository invitation model

* [WIP] tests

* [WIP] tests; fix overloads for client

* change GetAllForCurrent; suppress message

* some more tests

* [WIP]

* [WIP]

* add collaborator request model

* change return types

change return types for invitation methods. add permission attribute for
repository collaborators invite method.

* add some more tests

* fix xml doc

* check for null arguments

* fix tests

* some fixes from @ryangribble

* add parameterless constructor for RepositoryInvitation

* change setter

* change constructor

* fix merge conflicts

* [WIP] RepositoryInvitationsClientTests

* fix api url xml

* change collaborator request constructor

* change unit tests for collaborator request

* change repocollaboratorsclient

change overloads for add in invite methods to set permissions

* [WIP] integration tests

* add methods for interface

* NotFoundExceptions

* add overload for invite method

* rename repo property

* gramar

* overloads for observable repo collaborators client

* change integration tests

* new integration tests

* add decline test

* add test for accept invitation

Octokit/Http/ApiConnection.cs

@@ -387,6 +387,20 @@ namespace Octokit
             return Connection.Patch(uri);
         }
 
+        /// <summary>
+        /// Updates the API resource at the specified URI.
+        /// </summary>
+        /// <param name="uri">URI of the API resource to patch</param>
+        /// <param name="accepts">Accept header to use for the API request</param>
+        /// <returns>A <see cref="Task"/> for the request's execution.</returns>
+        public Task Patch(Uri uri, string accepts)
+        {
+            Ensure.ArgumentNotNull(uri, "uri");
+            Ensure.ArgumentNotNull(accepts, "accepts");
+
+            return Connection.Patch(uri, accepts);
+        }
+
         /// <summary>
         /// Updates the API resource at the specified URI.
         /// </summary>