For the IY->BC move, of course.

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.

Also, I've run VE on the TRS-80 for the first time! It doesn't work
well though. Screen is mostly blank all the time.

I removed instructions from the recipe which became obsolete when
Collapse OS became 100% bootstrapped. Also, I've updated instructions
to change the NL override which is necessary for blkup to work.

This would allow things like temporary giving control to the *CL
line on the TRS-80. For example... A very far fetched example. Not
at all the only *raison d'etre* of the layer...

I'm reserving the 100-200 range for non-bootstrapping needs.