0.3.1 Release

TODO:

* [x] Update `setup.py` version
* [x] Update AUTHORS
* [x] Update CHANGES.md https://github.com/flask-restful/flask-restful/compare/0.3.0...0.3.1
* [ ] Git tag new version
* [ ] Upload to [PyPI](https://pypi.python.org/pypi/Flask-RESTful/0.3.1)
    * [ ] `source`
    * [ ] `wheel` :)
* [ ] Update RTD.org default version