Pure transform DOM renderer

Fixes #35.

This pull request uses CSS transforms only in the DOM renderer. Performance on mobile devices is noticeably improved.

Note that some browsers have bugs related to CSS transforms, which lead to visual gaps between the tiles, notably WebKit when using `matrix()` (but `matrix 3d()` works perfectly) and Firefox (both `matrix()` and `matrix3d()` causes visible gaps at some scales/rotations).

Zooming out causes white flashes, we probably need to add some sort of double buffering, and maybe run the interim tiles algorithm in the other direction as well.

In theory, IE<=8 provides sufficient functionality (using [Matrix Filter](http://msdn.microsoft.com/en-us/library/ms533014%28VS.85,loband%29.aspx)), but this has not been tested.

Note that this work is based on #97, which should be merged first.