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.

This was becoming heavy to manage.

This is the first commit I do entirely in VE. It's a habit I'm planning
on taking as it helps a lot to find usability issues.

Pushed all words directly interfacing with ports and memory offsets to
low level layers. This saves us the need for keeping those variables in
runtime memory.

On the emulator of course...

Gave more priority to CPU in the emulator because initialization would
otherwise be horrendously slow.

I need RSHIFT and LSHIFT first...