Improve Transform2D

I worked on a few additions to Transform2D the other day and thought I'd share them.

As written in one of the commit messages, I'm unsure of why there is so much commented out code in Transform2D -- is it from an older version of the whole Graphics API?

I'd love to see this module improved along with a Transform3D.

A Transform2D would also be usable to switch from e.g. window-coords to collage-coords (as being discussed on the list), so mabye the function toCollageCoords (or a more generic version) would belong here?