typo
add unit tests for ncdc.gsod module; closes #31
cleanup gsod file fetching: use shared util methods
simplify gsod.get_data signature: start_date -> start, end_date -> end
allow ncdc.gsod.get_data() to accept a single station code
rm unused function
convert begin and end values for station dicts to python datetime.date objects
fix minor rounding issues with float values
allow gsod station queries to be limited by state, country, fips codes and date ranges