Add an example for Animatic and several easing functions

Created a very simple scene showing the Moon rotating about the
Earth. The animation is created using a function called `rotate`
built using an animate call and tail-recursion.

There are now several eased-versions of animation:

- `animate`: Even speed from start to finish.
- `ease`: Softened start and finish.
- `spring`: Elastic motion that springs about the end-point.
- `bounce`: Similar to `bounce` but does not go beyond end-point.
- `snap`: Rapid acceleration early.