This was becoming heavy to manage.

(well, not PC@ and PC!, but I'm not even sure what would be the role
of these in a PC/AT. they're only used in drivers on the z80 front,
so they will not be immediately needed. todo... )

Now comes the fitting part.

8086 asm is a lot terser than z80... Those indirect memory operations
are very handy.

Not comparing strings yet. Without asm tooling support, it's a big
chunk to swallow at once. It's progressing well!

Verified against nasm with equivalent code.