Added pubsub functionality

[jasongoodwin]

Added pubsub functionality - see test cases for usage.

Notes:

• The API should be unchanged.
• Request was made abstract and two implementations were added - one for pubsub. An additional apply was made on the Request object that still allows concrete requests to be produced with either strings or bytestrings to maintain api compatibility.
• Removed code where Bytestrings were being created from strings for Request instantiation as it is unneeded.
• organized the imports a bit removing unused imports and ordering them similar to the style guide's recommendations.

Let me know if you want any changes before approving pull request.

Thanks, -Jason

[jasongoodwin]

I'm going to close this and submit another pull request without changes to the api. After considering this for a bit I don't think it's necessary to touch the api at this point.