PROTON-471: Add Messenger->work to Perl bindings

Added methods for checking that a Messenger instance is blocking. Also
added asynchronous examples for Perl.

Added a recv_async and a send_async example app for Perl, based on the
Python apps.
PROTON-471: Example for Messenger->Work in Perl.
PROTON-471: Reworked how Perl processes error results from API calls.

It does not die on qpid::proton::Errors::INPROGRESS.
PROTON-471: Removed the bool mapping for arguments in the Perl bindings.