Wumpus

Copperbox revision 681.

At last! Decent arrowheads for curves and solved by my favourite method.

The method is to really just functional decomposition - but the decomposition should be so small that the parts are obviously correct[1] and the parts should correspond to catalogued functions whenever possible (by catalogued I mean functions that exist already, say in a geometry text, rather than my own invention). In this case getting decent arrows was largely a case of recognizing I needed a bisector function that returns the besecting vector between its two arguments.

[1] I'm careless here, as I haven't been systematic in my handling of angles. It might be that angles greater then 180 degrees will cause me problems. But they do look correct...