wumpus-drawing

Copperbox revision 2027.

I've reworked point generating chains. The new code is much simpler - no special encoding of a unfold, but it can support the same functionality.

The only apparent problem is that it needs to support two different drawing styles, thus it needs two sets of unzipping "run" functions. These functions are not suitable for a type class, and the current names are not appealing.

Copperbox revision 2028.

Adding a new chains example that should have been committed last time.