🔥 Features
* New CLI command `yahoofantasy shell` - open a Python interpreter with access to your yahoofantasy context object
* New CLI command `yahoofantasy clear-cache` - empty the cache of leagues, teams, players, etc but maintain auth data
* `league.past_league_id` helper property to get a league's previous season (thanks joeyagreco and brian-dev8 for the help!)