added twc kbdi drought index
fix file path
reversed kbdi max and min
added tests for twc/kbdi
remove national.txt and hardcode FIPS codes
change county_fips to county
added note about default end date
avoid reset_index pandas 9.1 bug in as_data_dict
fixed docstring
fixed typo in docstring
Merge pull request #40 from dharhas/kbdi

Added twc/kbdi drought index + tests