Adds KeyframeProperty#detach.

Consolidates Actor code to use KeyframeProperty#detach for property
removal.

Squashed commit of the following:

commit eb5410d830b0fa1367e40c5e43b8f1c842412462
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sat Mar 29 14:20:06 2014 -0500

    Cleans up docs and bumps version to 1.2.0.

commit 0a32f4a39df06a220e299c0b02aece9594b72184
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sat Mar 29 14:04:35 2014 -0500

    Adds unit tests for .detach and removeKeyframeProperty event.

commit f363954221828e7711bcbc6ebd9d4acc54377f58
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sat Mar 29 13:43:43 2014 -0500

    Adds KeyframeProperty#detach and cleans up Actor code.