Imported a packaged pure python implementation of the porter2 stemming algo. This replaces the weak stemmer originally used, though that code is only commented out at this time. This version neccesitates a new dependency: the 'stemming' package. To install this using Minicondas commonly used pip package manager run 'pip install stemming'. If you're missing pip, simply run conda install pip from the command line in your Miniconda directory. Note the purepython implementation is approx 100x slower than the python wrapper for the C code normally used in SNOWBALL and thus should be avoided for use in production code.