rnyang/STAHP — pull request #4 by fpinter (2014-08-25 04:00:17+00:00)
Title: added generate if, fixed use if, made row condition more flexible

First attempt at adding if conditions to generate, using `.loc` (and lots of `eval`) in pandas. Fixed use to allow `use if ... using filename`. In the process, split `row_condition` (just parsing stata conditions into pandas conditions) from `if_filter` to make using `.loc` easier.