A number of improvements to the Rackspace Cloud Queue Inputs/Outputs

1. Codec parameter is unnecessary as Rackspace Cloud Queues mandate
   JSON encapsulation.
2. Add ability to specify grace period in input
3. Add ability to specify a polling interval in the input (to limit
   the number of API calls per second).
4. Expand on the documentation for config parameters.
5. Add buffering to the output, although this doesn't take advantage
   of the Cloud Queues API being able to post multiple messages per
   API call as the underlying Fog library does not support that.
6. Add the ability to sprintf the queue name on output.