Coveralls

This commit is for [coveralls](https://coveralls.io) integration.  If it not needed, just close the request.

@tdryer will have to enable it for the repository.  It's already tied to Travis, so that will be the only thing needed to be done.

It will analyze the ```hangups``` package for unit test coverage and output the results in the badge I added to the README.
coveralls can be moved to the `tests_require` list.