wumpus-drawing

Copperbox revision 2149.

I've re-worked Chains so the types are simpler and they aren't prone to "none productive" chains.None productive chains were chains that didn't generate any points but now Chains have an iterative formulation so they always produce as many points as needed.

Quite a bit of code may be broken, though I have updated Grids - currently they have a problem that the exterior lines can be drawn twice.