Wumpus

Copperbox revision 632.

As the writer monad PostScript is no longer really the essence of Wumpus (i.e. Wumpus is now more about geometry and generating PostScript is relegated to a display technique) I've renamed the Wumpus module to PostScript in Wumpus.Core. I've also prefixed all the PostScript commands with ps_ to emphasis their imperative nature - they do actions to change the graphics context (state) rather than manipulate geometric objects.