Adds Bezier extension.

Squashed commit of the following:

commit 116ec7d08ab0bb17a8d0bb581e555563b22b5ca8
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Thu Sep 12 16:03:13 2013 -0500

    Builds 0.12.0.

commit 110414e4c61748c4d3ec78c62086cb8c008773da
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Thu Sep 12 15:50:32 2013 -0500

    Adds test for unsetBezierFunction and adds some documentation.

commit b13d7fb0c2ad8aef835e9380a7978afa1083678d
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Thu Sep 12 15:31:31 2013 -0500

    Adds Bezier tests.

commit e66ca38f2d7a6595c0f421fb576800c87e06bb0d
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Thu Sep 12 15:01:42 2013 -0500

    Adds static Tweenable bezier methods.

commit b62b48018250f53a12a1516e1b79fd24e6b64a05
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Thu Sep 12 13:27:16 2013 -0500

    Ports Bezier code from Scripty2.