Localize variables

All variables references through constants.py now referenced
through Calculator object for better encapsulation

Fixup in 91 test data because MIdR should have int64 type, not
float64 as in test data

fixes to test.py so it outputs a full CSV file when run against
PUF
change 'c' to 'p' to avoid confusion
Merge branch 'master' of github.com:OpenSourcePolicyCenter/Tax-Calculator into move_globals

Conflicts:
	taxcalc/tests/test_calculate.py
	test.py
Merge pull request #70 from talumbau/move_globals

Localize variables