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
> is there a good way to findIndex from right to left?

No, sorry. 

>  Is there a performance difference between these two examples?:

Not sure, the former only does an object allocation once. The latter does an allocation on every iteration. If `keyFrameIndices` never gets out of that scope, it will be discarded sometime soon after the callback function is done.