Adds CSSRenderer module.

Squashed commit of the following:

commit 7621be98ce396b5d7cef3f57b4e96572fd51f554
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun Jul 21 22:15:35 2013 -0700

    Inits CSSRenderer correctly.

commit 897c8c042163ab7e7a17da561bfcb4a28b589672
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun Jul 21 19:09:22 2013 -0700

    Updates CSSRenderer docs.

commit 9b9504a056ba44d89ec6e8e562f66af3522f8628
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun Jul 21 18:45:29 2013 -0700

    Adds API docs for CSSRenderer.

commit 12645865f30d174fd26adb0faebd1fc57cece216
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun Jul 21 18:05:09 2013 -0700

    Adds play-many-actors.html and fixes some stop issues.

commit 66163fccf4052a0050d63079400e1f02a250f27a
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun Jul 21 15:58:28 2013 -0700

    Adds gotoBeginning functionality to css.stop.

commit cf9856877dba4578cea1fc7815aeb26358bfe878
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun Jul 21 15:36:49 2013 -0700

    Implements stop and isPlaying.

commit bfd3901eb909c9e669c499c740b2db97a6a29942
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun Jul 21 15:19:33 2013 -0700

    Gets a CSS animation to play.

commit 33b458e4c788a2b2e2ab8d2738d6cdd2109e11bc
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun Jul 21 12:32:19 2013 -0700

    Hooks up sandbox to APIs, changes APIs to be consistent.

commit 4b78f2bffb734feebe38c5373346f19b708b7fb4
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun Jul 21 12:22:17 2013 -0700

    Adds stub for playCSS sandbox.

commit f931d216ca0df408ba32c3d6e0da172bbca92a18
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun Jul 21 12:16:36 2013 -0700

    Adds object outline for CSSRenderer.