Initial refactor to draw onto Graphics.img if not null.

Text is completely broken right now, though.
Missed switching to use c in some places
Hack to always draw strings on the main canvas. Fixes issues with text.
Merge pull request #58 from fzzzy/draw-offscreen

Draw offscreen; fixes a lot of graphics glitches. Crazy golf renders properly.
Revert "Draw offscreen; fixes a lot of graphics glitches. Crazy golf renders properly."
Merge pull request #59 from andreasgal/revert-58-draw-offscreen

Revert "Draw offscreen; fixes a lot of graphics glitches. Crazy golf ren...