Change to things to make performance testing easier

Change to things to make performance testing easier

- Saving of CPU and GPU BMPs
  - OverlayBMP doesn't overlay a BMP which is good because we don't want it to...
- SVG loads in centre of view
  - This will break the Quad tree, probably
- tests/bmpdiff allows us to quantitatively compare output bmp images.
  - I didn't say it was a good metric, there's just a metric now.
- Arguments to set rendering and transform type, argument to set maximum number of frames to render,
	argument to turn off the lazy rendering.

Will make some kind of ipython notebook next I guess.