not needed

The address returned in the error condition would be off by one.

I'm not sure why I chose null-terminated initially. Probably because
the z80asm version had null-terminated strings.

Length-prefixes strings are the traditional form of strings in Forth
and it's a bit easier to work with them with traditional forth words
when they're under this form.

I'm planning a string reform and it's standing in the way.

I'm planning on going back to 8-bit branching. 16-bit br cells incur
a non-negligible penalty and, while at first 64 words (128 bytes
forward or backward) seemed a bit limiting, I now don't see why one
would ever construct such a big branch. It would be un-forthy.

Also, I looked at using BC instead of IY to hold IP and the transition
would be a lot easier with 8-bit branching.

In this commit, all I do is add overflow checks in IF. The mechanic
below doesn't change. I'll give myself some time to think it over so
that I avoid yet another back and forth.

Prebiously, when encountering an error during a : ; definition from
input buffer, because the input buffer wasn't flushed, we would continue
interpreting and quit the whole program when encountering ;.

VI, here we come!

Writing directly to forth.bin seems to cause problems in some
environments such as Travis CI.

it was broken in the move to ncurses.

This will allow us to implement AT-XY, paving the way to all sorts
of nice new things.

Read the contents of forth.bin at runtime. This allows us to get
rid of the bin2c tooling.

Instead, embed absolute path to blkfs. Having to rebuild the stage
binary at every change in blkfs is getting tedious.

It doesn't change anything featurewise, but this change is in
preparation for the addition of an eventual AT-XY.

Use EXX instead of the stack for HL protection and remove all
spurious uses of chkPS,

I wanted to inline chkPS in next because of its "tight loop" status,
but for reasons I don't understand, doing so breaks Collapse OS.
Later...

It's small enough to be worth it.

So far, the resulting binary matches.

and renamed it "Core words". Also, reworded the presentation.

It was ill-advised.

I hadn't noticed that this word was almost ANS compliant.

Instead of letting each configuration taking care of RDLN$ and
"CollapseOS" prompt, move this to BOOT to simplify xcomp units.

Initialization source code is now only for driver initialization.

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

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.

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.