Merge pull request #188 from bepetersn/v2.0-dev

VS 2.1.1 -- created one possible version of the DailyPopulationChanges model; integrated with GET and POST
change underlying data format from json to csv; ALSO implemented dynamic formatting methods for model
Merge pull request #189 from bepetersn/v2.0-dev

VS 2.1.1 -- DailyPopulationChanges (DPC) model, POST API, tests for both
fixed very silly error naming csv files .json
changed name of testing env var to CCJ_TESTING
Merge branch 'v2.0-dev' of https://github.com/sc3/cookcountyjail into v2.0-dev

Conflicts:
	ccj/models/daily_population_changes.py