Setup continuous integration

[danieldeutsch]

There should be some continuous integration setup, like Travis CI, that runs the unit tests every time there is a pull request to master.

This could be hard to get working for all of the unit tests because, right now, some of them use proprietary data that can't be added to the repo and some of the metrics require using their own conda environments. I think a good first step would be to just get the basic unit tests working, and the more complicated ones can be added later.