Fixes behavior of single-keyframe animations.

Changes behavior or undefined keyframe states.

Squashed commit of the following:

commit 3146b6a80605958a619d42dc066c491f82ccac6c
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Tue Apr 8 21:28:55 2014 -0500

    Adds upgrade notes for 1.3.0.

commit 4781f39b7f4b22c969c5b872867243f7693e59df
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun Apr 6 17:45:22 2014 -0500

    Revs and builds 1.3.0.

commit 6961331331448853d083cddf6f47774c3766e188
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun Apr 6 17:34:28 2014 -0500

    Removes null check.

commit 2d9a9e19f3fcd572f64acc65fc481ab36a162847
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun Apr 6 17:31:28 2014 -0500

    Removes an unnecessary condition check.

commit 74d44291f9e9e74fa140ee065c29a80cbeb44761
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun Apr 6 17:14:37 2014 -0500

    Updates failing tests.

commit a50685fd609e976c573f75a464ab991ef3af055e
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun Apr 6 14:30:28 2014 -0500

    First-pass fix for broken single-keyframe behavior.

commit b3f2792bdec04075a11a41796fb0d7f89890f138
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sat Apr 5 17:25:49 2014 -0500

    Builds 1.2.1 binaries.

commit 60447c31e3c2cb2ebf691e2dcab1267f4db644b9
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sat Apr 5 17:09:47 2014 -0500

    Makes newly-added fill-in test pass.

    Updates old, related test to not expect a null value.

commit 659593ec6393ee63d9aa6df5f2f1427577ab5625
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sat Apr 5 16:28:38 2014 -0500

    Adds failing test for not-yet-reached keyframe calculation.