Alpha tween now affects itself and all its children.

Hi Russell, it's Leong here. I emailed you sometime ago with a short message thanking you for the LeanTween plugin. I came across something that I needed to fix, and I thought you'd like to add this fix to the master branch. I made it so that the "alpha" method now tweens the alpha for itself and all its children (including nested children). I didn't fix the "color" method since I didn't need it, but it would've been similar. Hope it helps. Let me know if I did something wrong (e.g. inefficient coding), I'm still learning. :)