Handful of small changes

These changes mostly involve stopwords lists, how sentences and phrases are split, and how numbers in the text are scored.  This addresses some less-common cases found when processing news articles, which were resulting in unwanted keywords and/or keywords that were scoring higher than expected (for example because keyword phrases with more words are generally scored higher.)

These changes did not change the behavior of the core algorithm, and the results for the sample text are still consistent with the canonical results (except for a few small differences caused by the choice of keyword list, described in the comments.)

Let me know if you see any issues, or if you want anything changed/modified with these before accepting.