a working binary grammar of number
in the process of generalizing to next, but stuck on explanation graph cycle detection
Merge branch 'prism' of github.com:joshrule/GrammarInduction
Changes to draft and initial bib file for draft.
Various changes to BuildNumber.hs and Prismify.hs.

Prismify: fixed acyclicity check and changed main goal to take a list of target data goals rather than a file containing data goals.
BuildNumber: added a NextSentence rule. Also added functions for generating train/test data splits and spitting those out into files for prism consumption.