Previously, calling quit would break EOT behavior and not properly
quit Collapse OS.

Verifying that forth.bin is stable is enough. Also, fix shebang.

During "make updatebootstrap", we use less than 0x20 bytes on the
PSP side and less than 0x40 bytes on the RSP one. 0x100 bytes ought
to be enough for anybody.

Use straight VARIABLE instead of Z80MEM+. Initially, I used this
system to allow z80a to be embedded in a system binary, but now
I don't think it's worth it. Compiled, z80a is 2.5k. Sure, it's a
sizeable amount of RAM, but I think that even with it in RAM, I'll
manage a bootstrap within my most constrained machine, the SMS with
8K.

Not worth the trouble. Easier to set jump in binary directly.

It's now much easier...

Finally got rid of the XPACKed core and managed to cross-compile
all core words, which greatly simplifies the bootstrapping process.

Saves us an (ok) indirection and will save us more soon.

This should allow me to simplify LOAD's exit mechanism on block
end.

My mind is getting forthy.

This allows me to reclaim some RAM I hadn't even noticed I
needlessly monopolise.

Now that this section is so small, I think I can see a possibility
for cross-compiling Collapse OS entirely, which would be great
because we could get rid of the relinker.

That INIT thing is unnecessary.

Makes xcomp.fs units shorter.

TODO: implement X['] so that I can remove those XCURRENT patterns.

Now more low/high layers.

This leaves space for xcomp-core which is growing.

This allows us to move words like ABORT" to xcomp-core, which is
I think the last roadblock before being able to unify all drivers
into a single xcomp layer.

No more low/high

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...

This makes [entry] much simpler. Also, remove unused LITS word.

And refreshed description.