Add a class for custom Json renderer.

The custom renderer adds the ability to handle unexpected responses by checking
the value of the return value from the controller method.  This allows for
setting different http status codes (such as 404) instead of just the 400 or
500 that wsme allows.
Merge pull request #24 from slagle/json-renderer

Add a class for custom Json renderer.
Merge pull request #26 from mtaylor/heat

Initial HEAT template generation work
Added Relation for Rack Resource Class
Allow setting ResourceClass on Rack