Filter stop words from feature set using nltk stopwords corpus
Fixes a bug in which positive posts in the testing data set were being associated with negative labels.
Filters out stop words, performance is still poor

Almost all negative posts are still being labeled as positive.
More graceful tokenization of posts; classifier still not performing well.
Filter out low frequency words from feature set

Lower false positive rate, but manual inspection via the
interactive_sentiment script suggests that performance is still poor.
Merge branch 'master' of https://github.com/paepcke/forum_viz