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.
`line_length[current_line]` is being used a lot here. I would assign it once to a variable e.g. `current_line_length = line_length[current_line]`.