Use _check_for_usgs_error to ensure the USGSAuthExpired hint will be shown if an expired API key already exists. Also add a docstring to explain how login and logout affect the stored API key (#62)
Use _check_for_usgs_error to ensure the USGSAuthExpired hint will be shown if an expired API key already exists. Also add a docstring to explain how login and logout affect the stored API key (#62)

kapadia/usgs