add support for additional variables to cpc.drought dataset
add unit tests for cpc.drought
add note to changelog about cpc drought
add basic unit test & framework for cpc drought dataset
add changelog note about ncdc.gsod changes
add changelog note about date and datetime parsing
Merge branch 'cpc-drought'

Conflicts:
	CHANGES
minor doc fix
clean up cpc.drought tests: use a mocked data file
change cpc.drought.get_data() kwargs: start_date -> start; end_date -> end to be consistent
replicate tarfile.open()'s context manager for python 2.6 support