Big refactor in anticipation of eventual viz needs -- products are parsed into NLTKProducts, comprised of NLTKReviews and subsequently NLTKSentences. NLTKSentences keep track of interesting word types, the word and how many times they appear. Similar summary info will be available for NLTKReviews and eventually NLTKProducts
Removed NLTKProductSummary class -- seems unnecessary now
NLTKReview instances are now summarized, next up is to summarize the entire product
Added some documentation to everything
NLTKProduct now has a summary