Nameko Release Candidate 2.9.0

[Jakub Borys]

Nameko RC 2.9.0 is ready for testing. This is a big one:

RPC reply queues are now set to expire rather than auto-delete, and are no longer exclusive, allowing clients reconnect. https://github.com/nameko/nameko/pull/504 It's now possible to accept messages in multiple serialization formats. Adds config-based mechanism for specifying custom serializers. https://github.com/nameko/nameko/pull/535 Enhanced environment variable substitution including recursive references. https://github.com/nameko/nameko/pull/515