adding the message description to error logging.  Closes GH-87
making the ExceptionHandlerBehavior able to look into the inners of AggregateException.  Closes GH-89
introduced HandlerChainPolicy as a convenience for writing policies against HandlerChain's within a BehaviorGraph.  Closes GH-88
added the convenience methods for registering exception handling rules to HandlerChain.  Closes GH-90
having ChainInvoker close the nested container at the end of executions.  Kind of absolutely, vitally important.  Closes GH-92
made the necessary changes to make the retry now continuation and error handling policy work.  Closes GH-91