Created ParallelForwardingAppender, AsyncForwardingAppenderBase and associated unit tests for ParallelForwardingAppender.
Use ConsumingEnumerable in ParallelForwardingAppender, modify tests to not be time or exact quantity based where possible.
Make ParallelForwardingAppender Disposal more robust.  Add missing test Task disposal.  Add missing RingBuffer test cancelation token usage.
CompleteSubscriberTask on unknown exception in ParallelForwardingAppender SubscriberLoop().   Remove use of cancelation token in task.wait during task completion.
Merge pull request #4 from rcollette/master

Created ParallelForwardingAppender, use volatile modifier on shutDownRequested