Fades in the animation with the name animation over a period of time defined by fadeLength.
If the mode is set to PlayMode.StopSameLayer, animations on the same layer as animation are faded out while animation is faded in.
if the mode is set to PlayMode.StopAll, all animations are out while animation is faded in.
If the animation is not set to be looping, it will be stopped and rewound after playing.