The previous approach of maintaining R> and W> pointers was
conceptually simple, but made INT handler code actually quite
complex.
Now, we maintain indexes instead. It's much easier to perform
bounds checks and to compare for equality, something we have to
do quick in the INT handler.
it seems I left my asm argument harmonization half done here.
Instructions list at B208 doesn't correspond to many actual
mnemonics. This mnemonic here was the worst offender.
Driver configuration don't need their own words at runtime, we only
need to compile them as literals when compiling words.
Now that we have this "declaration blocks" pattern emerging, it
seems like a good idea to take advantage of this in drivers, both
for simplifying the xcomp unit and to make final binary slimmer.
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.
