Implement simple SVG animations via Web Animations

This code illustrates how simple SMIL animation elements with no timing instructions (other than duration and repeat count) can be handled directly using Web Animations.

For now, we assume no events or sync-based dependencies.

Test with the Blink CL that has native animation elements disabled -
https://github.com/smil-in-javascript/blink/pull/2
Simple animateMotion path support

We now support trivial motion path animation, where the user explicitly
specifies the path.

We don't yet support most of the options supported by animateMotion (or
the other animation elements).
Merge pull request #4 from ewilligers/simple-from-to

Implement simple SVG animations via Web Animations