Rewrite of scheduling code.  Adds support for requestAnimationFrame.

Drops support for custom FPS.

Squashed commit of the following:

commit 5e30d69556488eebf595803f3c17f4078c37b268
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Wed Aug 28 21:05:29 2013 -0700

    Builds 0.10.0.

commit caf287ebd9c87c3ddacd55dd48ed85bf26726337
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Wed Aug 28 21:00:29 2013 -0700

    Fixes Node compatibility, fixes final step call and kills FPS.

commit 8f11b5d04cab698504713d76f16be292c33ce576
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Wed Aug 28 20:36:03 2013 -0700

    Fixes step call misplacement.

commit 985faf3742262fcf79e62eb63c699b00c8781f2b
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Wed Aug 28 20:24:57 2013 -0700

    Initial pass at rAF implementation and some other cleanup.