We initially used Cairo for its bezier flattening algorithm. That
algorithm turned out to be a bit too imprecise at the scales we're
working at here (#17), so I ended up porting over some code from
Antigrain Graphics. The only other thing we used Cairo for was debug
output and coordinate transforms, so I just wrote the relevant vector
math in a small header file, deleted all debug output code and thus
eliminated the cairo dependency. This is a step towards Windows builds.
