Added elastic easing
Added elastic easing

Adapted from
https://github.com/HaxeFlixel/flixel/blob/dev/flixel/tweens/FlxEase.hx

playedonline/flambe,weilitao/flambe,Disar/flambe,markknol/flambe,weilitao/flambe,Disar/flambe,aduros/flambe,Disar/flambe,mikedotalmond/flambe,aduros/flambe,weilitao/flambe,weilitao/flambe,mikedotalmond/flambe,mikedotalmond/flambe,Disar/flambe,playedonline/flambe,markknol/flambe,playedonline/flambe,mikedotalmond/flambe,aduros/flambe,markknol/flambe,playedonline/flambe,aduros/flambe