The new algorithm is an iterative one with an arbitrary threshold for splitting
curves. It splits curves evenly. This should theoretically be less accurate
than the existing recursive approach, but seems to give subjectively better
results in practice.
I'm planning to make this a minimal-allocation TTF parser. This will
speed up start-up time for applications, but have some overhead for
rasterizing glyphs. Which should be okay, since rasterized glyph bitmaps
should be cached anyway.
This commit just adds the loading of the HEAD table.
