wumpus-core

Copperbox revision

I've changed the internal Picture representation to fix the unit to Double (PostScript point) rather than be parametric.

The previous changes to better support units didn't actually improve matters for Wumpus-Rhythm, so I've been re-thinking the types in their entirety. The first result is I no longer think Picture, PrimPath etc. warrant being parametric by unit. As they are final types - used for generating output, opaque and only marginally transformable - it looks like they can be fixed to Double without loosing any functionality. This simplifies Wumpus-Core - no need for the DUnit type family hack; and it stops the Picture types being artificially functorial. The downside is that Points in drawings will need more type annotation.