New functionality from all forks

Dear mjpizz,

Various people have forked this module and built on it, including me. This pull request is all subsequent work. As of the latest commit, it is now tested against v4 of the API and has additional functionality for activity, tasks and moving stories. Please could you merge and update the pypi entry; as of now 0.0.3 doesn't work because it points at the v2 API, which Pivotal has retired.

If you would like someone to adopt the package I'd be happy to do so.
What's the reason for using empty string here?