fix small bug in testhandler and improve it

* Docs about how to use it
* Have it bind to *all* messages, not just `*.*`
* Deprecate the `get_topic_blah_blah` for a more streamlined API
Merge pull request #9 from stitchfix/feature/expand-and-document-test-handler

fix small bug in testhandler and improve it
bump version
Merge remote-tracking branch 'origin/master' into queue_messages_for_batch_delivery
stop creating new instances