Poor small chart and wumpus-clave

Copperbox revision 1420.

Minor corrections to PSC - including a bug fix on rectHeight that was making labelled Y-axes draw incorrectly.

Also, I've started a new project wumpus-clave to draw percussion notation in box notation (often seen in Godfried Toussaint's papers on clave rhythms and in Simha Arom's African Polyphony & Polyrhythm book).

Chart drawing with PSC had become a very frustrating way of working out how to make drawings with wumpus-core. Charts are too various with too many configurations, so drawing them distracted from finding out good "mid-level" abstractions above the low-level primitives of wumpus-core. Clave patterns are much simpler, so should be less distracting.