Add support for animating CATransform3D

[NickEntin]

This adds conformance for CATransform3D to AnimatableProperty by decomposing the two matrices into their respective components, interpolating the values in the decomposed transforms, then recomposing the interpolated value into a CATransform3D. This follows the same pattern we use to interpolate CGAffineTransform.

Resolves #19.

[NickEntin]

I also tried a version of this using simd types, but it had worse performance (by ~15%).

[seanho]

I do not understand most of the math stuffs in there, just reviewing the change set as is and code looks good. The test snapshots are very useful and cool, one suggestion, if we can make the red block different color on each side, it will make the rotation/perspective snapshot animation more obvious.

[NickEntin]

one suggestion, if we can make the red block different color on each side, it will make the rotation/perspective snapshot animation more obvious.

That sounds like it would be super helpful, but as far as I know CoreAnimation doesn't support this. Layers are really 2D objects in a 3D world, so there is no "back side" to the layer.

[NickEntin]

as far as I know CoreAnimation doesn't support this

Chatted offline. I misunderstood what the suggestion was. Commit coming shortly to address this.

[NickEntin]

So... the last segment of the shear interpolation test looks really weird. But it's actually doing the right thing. I'll replace it with a better example.