wumpus-extra

Copperbox revision 1320.

I've reprieved Grid from being in the Wumpus.Doodle name space - its now back in Wumpus.Extra although its renamed Matrix to be more familiar to the name from TikZ.

I've put in some work generalizing it so that I'll be able to add a monadic operation to bind lines to cell coordinates. This will mean making the writer part of the monad handle accumulating lines, which is currently missing...