RPC: docs and namespaces

This blueprint aims to enhance the existing usage of oslo.messaging to make the
version scheme more clear to developers.  Several people have expressed that the
current code is difficult to understand, so this spec aims to improve that.

Spec for blueprint rpc-docs-and-namespaces.

Change-Id: I19f691708e038ad0140ee1a14409da59be998f1d
Merge "RPC: docs and namespaces"