First Commit of Animation

Here it is.

I'm feeling pretty good about the API but the real test will be when someone other than me ports to it or builds their own bot with it. 

If anybody is willing to try this out I will bend over backwards to help them. I need the perspective of someone who is new to it.

I've got some basic documentation over in docs/animation.md but it's not really written well for beginners. Once the API is golden I need to write a wiki page that's more of a tutorial. There is a lot to digest here.

This PR is the culmination of all the discussion in #304 also fixes #362
Thinking out loud... "center" vs "isCentered" seems like a directive vs a request for state. These are being passed on instantiation in which case the former makes sense, but if a user is requesting the state the latter makes sense. Should the opts accept "center" (status quo) and then we add a getter for "isCentered"? I realize the getter is getting a public property, but the API surface is improved and backwards compatibility is maintained. 

Oh wait! That's a bad example. "isCentered" sounds like we are asking if last.degrees === (range[0]+range[1])/2