With KEY and EMIT being switch words, most of the high layer can
be defined before drivers.
In addition to this change, I've compacted core blocks which were
becoming quite sparse.
There wasn't much of a reason to leave a loop early on 0x0d or null.
The idea was that once you have a CR or null, the rest is garbage
and you shouldn't see it.
However, it brought a problem: In VE, you couldn't insert characters
past that limit. It would be written, but never displayed. So let's
get rid of this logic and simply always display a 64x16 grid.
DO and LOOP now only compile words from stable ABI, which make them
suitable for xcomp. This will greatly simplify driver writing and
allow us to mostly avoid the low/high divide in drivers.
LEAVE is still xcomp-incompatible though.
This make us very very tight for "<0x100" limit for literal words.
Hopefully, we won't need more stuff in that area of the binary...
