Added a few statistical distances

Added Chi-square, Bhattacharya, and Intersection distances to compare distributions.
Do you have a reference? Do you know where this is useful? It's a weird measure. It's definitely not a distance, because if p and q are equal than the returned value is 1. Presumably the distance is 1 - Intersection (as defined below). Is there a better name than "Intersection"? I don't think the name is very clear in the context of a larger stat package.