Added a few statistical distances

Added Chi-square, Bhattacharya, and Intersection distances to compare distributions.
I don't think so. For things like Entropy and Kulback-Liebler it makes sense if p and q don't sum to one. Not sure about the other distances. Especially with floating point weirdness, I don't think we want to be super picky about it summing to 1. I think we can assume there are no negative values.