Pocketmine-mp: No way to set custom username rules

[ghost]

Issue

There is currently no way to set custom username rules. Player::isValidUserName uses hard coded rules no one can edit. It would be great if there was a way server owners can use a API to implement there own username policies without having to override the function by extending the player class. Or, possibly changing the $this->close to kick, so owners can cancel PlayerKickEvent.

[Goodsoldier]

I think it's necessary since My korean kids don't understand english.
PMMP only allows english username witout space.
But, PMMP doesn't allow korean user username even without space.