Implement Stomp-like unreceive and DLQ behavior in Stapfen::Client::JMS.

Issue #7
Add YARDoc to Stapfen::Client::JMS#unreceive
Merge pull request #11 from ismith/jms

Implement Stomp-like unreceive and DLQ behavior in Stapfen::Client::JMS.
Update the README to include newer DLQ support in JMS
Fixes for JMS support.