Add test coverage measurement

[sils]

Just measure coverage with pytest --cov and set up http://codecov.io/ or something will help monitoring tests. Really quick to do.

[sils]

Tried setting that up but for some miraculous reason the build for python 3.2 fails with a syntax error on my commit so I removed it, not continuing work on that since it's not like I don't have other things to do. :/