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.
This allows us to remove a lot of labels usage in boot code. This commit has no effect on forth.bin.