wumpus-drawing

Copperbox revision 2111.

I've reworked the Chain modules so the types are more like the other drawing types - i.e. the main Chain type has become a LocCF function.

The Grids module and some of the demos will need changing to work with the new formulation. Also the derived chains could be simplified, I re-wrote them quickly only to work at the new types rather than to do so elegantly.