Allow the potion effect caused by WitherSkulls to be cancelled along with damage cancellation (e.g. via events).
Optimize Player Lookup - #112

Optimize player lookup and various player operations. We mainly do this by keeping a map instead of iterating through all players. We also speed up the duplicate login check and a few other checks by simply checking for one matching player.

Thanks @aikar for some of the implementation
Change various "Nope!" kick messages to something more descriptive and less confusing for players.
Testing