wumpus

Copperbox revision 2176.

More work on unit conversion - I've added an automatic type specialization class Unit to Wumpus-Core, but in practice it seems to be less useful than I thought.

I've updated the UnitConvert module in Wumpus-Basic, however, the functionality here cannot handle contextual units (em, en, etc.). It looks like I'll have to add some interpretation of units to the Dislacement and DrawingPrimtives modules instead.