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.
Okay nedbat, but I might lose a lot of lines foolishly!
Michael, those are possible breakpoints. But I may find a better name. Anyway, those form the nodes of a DAG.