Agent-Worker Message now uses JToken payload and is sent async

As part of the cleanup for this change, Worker logging now transmits through messages instead of standard error and the standard IO reads/writes are now async.
#18 #20 addressed by this fix
@davidfowl @abnanda1  @intern-felicco 
The previous implementation had intermittent issues surfacing with the additional log traffic, likely due to synchronous reads completing with incomplete messages in the buffer. This fix introduces a delimiter to avoid buffering issues and makes the call asynchronous rather than blocking.