reverseAnimation(name) {
		if (typeof name !== "undefined" && typeof this.anim[name] !== "undefined") {
			this.anim[name].frames.reverse();
		} else {
			this.anim[this.current.name].frames.reverse();
		}
		this.isDirty = true;
		return this;
	}
reverse the given or current animation if none is specified
@param {string} [name] - animation id
@returns {Sprite} Reference to this object for method chaining
@see Sprite#animationspeed