Update .clang-format with new options from clang 3.5.
Export compilation database for use with YCM.
Add sparse_vector class.

This should be useful in several places where we want to use a sorted
vector of pairs to represent either a sparse vector or a dictionary.
Begin work on stats library for meta.

This is mainly to try to make it easier to follow things when we're doing
probabilistic modeling: instead of carrying around maps of parameters, we
should be using classes to represent the distributions themselves instead.
Port naive bayes classifier to use stats models.

(I think I've fixed a bug with it in the process, as it's doing much much
better now in terms of performance.)
Fix compilation with gcc.