Support for `setup.py test`, tox testing, and Travis CI.

I'm developing an automated test system for packages uploaded to PyPI, and I noticed that your package had tests that weren't being picked up because they were in a Makefile.

This patch enables you to run the tests with both [tox](http://tox.readthedocs.org/en/latest/) and with `setup.py test`.

I've also added a `.travis.yml` file, which, [if you enable Travis CI on this repository](http://docs.travis-ci.com/user/getting-started/#Step-one%3A-Sign-in) will automatically run the tests when you push to GitHub.

Your Makefile will continue to function as per normal.