Reading docs with a generator to save memory
Reworked caching to use gzip json instead of joblib
WIP: wired in new tokenizer that reads from json

Tokenizer API changed- returns just a parse tree. Need to adapt feature extractor now
adapted feature extractor to take parse trees
Updated tokenizer tests
Updated more tests
Reverted dfb80dfd48

Reading docs is lazy, but the resultant parse trees are all held in memory now
Fixed issue with token indexing