nameString: The name of the user stat
Returns a Integer represents the value of the user stat.
nameString: The name of the user stat
Returns a Float represents the value of the user stat.
nameString: The name of the user statvalueInteger or Float: The value of the user stat
Returns a Boolean indicates whether the method succeeds.
success_callbackFunction(game_id)game_id: The game which these stats are for
error_callbackFunction(err)
Stores the current user stats data on the server.