Adding lowess (locally weighted scatterplot smoothing) via cylowess, a cython port of the lowess function.

I originally implemented in pure python, but the speed was horrible with large datasets. Using a cython implementation improves the speed dramatically. In fact, even with large datasets response time seems instantaneous. This does create a new required dependency for cylowess, particularly livingsocial's fork. I underestand how this could create a problem, but if you tell me what your concerns are I'll do whatever is needed to address them.

Thanks,
Steve