v0.2.1

Bot AI improvements:

• In defence mode try to discard not needed safe tiles first
• If there is no not needed tiles, try to discard safe tiles that will do less harm to the hand state
• Don't call a riichi for a pair wait (except chitoitsu). This wait can be easily improved

Local games improvements:

• Don't allow to call ron when furiten
• Support multiple ron for local games
• Support abortive retakes for local games