Add FlxTimer.wait and FlxTimer.loop

[Geokureli]

Rather than doing

var timer = new FlxTimer().start(duration, (timer:FlxTimer)->onTimerComplete());

can do

var timer = FlxTimer.wait(duration, onTimerComplete);

similarly instead of

var timer = new FlxTimer().start(duration, (timer:FlxTimer)->trace('${timer.elapsedLoops} loops'), 10);

can do

FlxTimer.loop(duration, (loops:Int)->trace('$loops loops'), 10);