Refactored testing for Coveralls

I added support for automated test coverage reporting through [Coveralls](https://coveralls.io/). For it to you work, you need to login with your Github and activate it on this repository. Then whenever the build is pushed to Travis, it will upload the test coverage. And comment on pull requests too!

While adding this I refactored testing, removing nose. I removed the whole `tests` directory and the `run_tests.py` file, and moved the testing configuration to the command line, as you can see in the `.travis.yml`. I admit, its not as pretty as the nose testing, but I figured it was worth it, because of the simplification in the procedure.