0.3.1 Release

TODO:

* [ ] Update `setup.py` version
* [ ] Update AUTHORS
* [ ] Update CHANGES.md https://github.com/flask-restful/flask-restful/compare/0.2.12...0.3.0
* [ ] Git tag new version
* [ ] Upload to [PyPI](https://pypi.python.org/pypi/Flask-RESTful/0.3.0)
    * [ ] `source`
    * [ ] `wheel` :)
* [ ] Update RTD.org default version