wumpus-basic

Copperbox revision 2358.

I've added optimized mconcat definitions to the Monoid instances where I'd prefer the concatenation not to start with an initial mempty.

mempty is harmless for CtxPictures, LocGraphics etc. but these objects generally form blank elements that don't get thrown away until Wumpus-Core renders them - so I'd like to have as few around as possible. Also blank paths or text elements might not be strictly neutral, it's possibly they add extra blank lines to the output - something I've never properly investigated.