chkPS, used to be only for words that pushed back to PS, but I've
recently removed underflow checks from next and I forgot to add
missing chkPS, calls that go with this change.

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.

with uflw checks not being in next anymore, we can save ourselves
a forward jump.

Bring native words together, make the next/exec/does/compiled
cluster be at the beginning.

Next step: bring find code into _find word.

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.

The usage of numerotated labels for this was becoming severly
confusing.

Inline it in next and make chkPS, call a newly reserved label for
it directly, removing a layer of indirection. This frees a spot in
the stable ABI.

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.