first working python only lowess implementation... but it's slow
modified to have shorter inner loop and use scipy instead of numpy
only process every 15 and the last 5 data points
added lowess smoothing via cython version (cylowess) of the function
1) cylowess is now optional, 2) at lowess runtime check for cylowess, 3) if found use it otherwise use pure python, 4) pure python performance improved by new delta calc and skipping data for larger data sets
Merge pull request #538 from steveakers/master

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