Merge branch 'master' into develop
Fixed minor error in sample code.
Fixed NullPointerException when performing a Communicator request.
Added a static MainThreadExecutor to avoid numerous instances.
Added methods close & closeNow to Communicator.
Added documentation to new Communicator methods.
Added TODO notice to Communicator.close().
Resolved stuck thread in QueuedPool.promote() issue.
Improved Communicator's Thread interruption.
close() and closeNow() instead of stop() and cancel().
Formatting improvement.
Set project version to 0.6.1.
Merge branch 'release-0.6.1'