With KEY and EMIT being switch words, most of the high layer can
be defined before drivers.
In addition to this change, I've compacted core blocks which were
becoming quite sparse.
Adding a delay such as the 20ms one we have in AVR programmer's
initialization routine is tricky without a word like TICKS.
This implementation is highly inaccurate, but more accurate and
reliable than a "ballpark" DO..LOOP...
Also, move doc to doc/asm.txt.
Also, fix the pcat recipe which was broken since the overlay change.
I hadn't noticed it because I didn't have to rebuild the MBR.
