First draft of typesetting engine

I implemented the Knuth-Plass algorithm. If necessary, I can simplify the code (the current version may work for circle or triangle-shaped text, [see this example](http://www.bramstein.com/projects/typeset/) but we don't need such advanced use).

The PostScript part still needs to be done.
Would using `float('inf')` here be problematic? I assume you're only using this for comparison (and not a direct-equality check) -- although I guess I could wait until I read ahead to ask this. :)