Added module to handle rabbit policies [1]

Used quite a bit of the existing rabbit modules provied by @chrishoffman.

[1] https://www.rabbitmq.com/parameters.html
Cleaned up docs just a smidge

Mostly added periods where missed, and corrected /vhost spacing.
The setting of params via dict or string by tags

Updated per @mpdehaan suggestions.
* Rather than passing in JSON, supply the policy options as a hash
  or string.
* Bumped version_added to 1.5.
Handled string/dict the ansible way
Merge pull request #4957 from retr0h/rabbitmq_policy

Added module to handle rabbit policies [1]