wumpus-basic

Copperbox revision 1836.

I've added a new type provisionally called VecGraphic to Basic.Graphic.Base.

VecGraphic models graphics that take an initial point and return a new end point as well as drawing themselves. This is how text works in PostScript - drawing text takes the implicit current point (usually initialized with moveto) draws the text and adds the width vector of the text to the current point.

Unfortunately for Wumpus whilst this is a useful graphic type, Basic.Graphic.Base is becoming very ad-hoc with lots of similar but special purpose types. It would be nice if they were unified somewhat.