Faster b/f algorithms, bake additions

Lower slope and intercept for backward and forward algorithm element/time graphs (10x to 100x faster in tests). Bake now automatically will normalize out edges to have the probabilities sum to 1, and will merge silent nodes which have a 1.0 probability edge connecting them. Also added mixture models, fixed error in kernel density estimates and sped that up by ~30x. Added sampling from mixture models and kernel densities.