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...
Initially, I used the same letters as those used in the z80 ref
docs, but it makes the different assemblers harder to use than they
should. Having consistent "argtype" rules across assemblers should
help.
