AMQP 0.9 support, ->confirm, more care that all on_close callbacks will be
  called correctly, and potential memory leak fixes
include amqp 0.9.1 spec, duh
finish on_return at message, channel, and connection level
Handle flow control (do not throw messages away!)
Handle out-of-order CancelOk
Handle server-sent Nack
Add missing accessors, e.g. is_open and is_active and verbose
Fix a potential memory leak
Update tests to work with all new features, and test some of them.
Document spec xml files
fix on_return for non-confirm publish