wumpus-core

Copperbox revision 2180.

I've changed the Picture API so all the functions that operate with sizes are fixed to Double for the unit. This pushes supporting parametric units (or not) to clients, which seems sensible for two reasons. Firstly, the annotation burden with the previous function signatures was too high. Secondly, units need careful thought - so it is better to handle them properly in client code than present a half solution in Wumpus-Core.