add py unit tests
move python files to python dir
rename python class to Config
refactor python

Merged _helper.py into centroid.py, add tests, fixed an edge case, and
improved code.
config to string json
tabs => spaces
Merge branch 'master' of github.com:ResourceDataInc/Centroid
Merge branch 'py-improvements'

Conflicts:
	python/centroid.py
	python/tests.py