wumpus

Copperbox revision 1562.

Updates to Wumpus-Basic and Wumpus-Tree. Tree drawing to now uses radial anchors - this means nodes no longer need be opaque.

In Wumpus-Basic, I'm experimenting with existential anchors again. I didn't really like the previous design where dots could return differently typed objects that only supported taking anchors. The new experiment uses existentials again to get all anchors at the same type, but is a bit nicer than previous ones.