Implementing probabilistic KDE error bounds - Week 4

This week probabilistic KDE API has been integrated into the existing codebase and many unit tests have been implemented. All tests seem to indicate that this implementation is working well. After a review by Ryan, there are a few things to improve a bit but for the most part it should be ready.

Another possibility for further improvement is to reclaim unused error tolerance as explained in this paper. I am working on this for this week as well.

It was interesting to learn some tips on how to test pieces of code that depend on random parameters.