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.
Given that you're returning a list of `Item`s, it's apparent that objects of this type aren't just used locally to this method. Might it be better to assign `Item` in module scope?