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

Now that everything is cross-compiled, no need to XPACK. If we ever
need it again, we know where to find it.

Now that the boot binary is fully cross-compiled, there's no use for
the linker anymore. Theoretically, it could still be useful, but I
can't think of a real use case.

Let's take it out of the picture. If it's ever needed again, I'll
know where to find it.

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...

Now that adev is directly in core, things are easier.

It's small enough to be worth it.

Also, fix PSP leak in font compilers.

The keyboard is a bit glitchy, but these are the same glitch as those
that were already present in Z80 Collapse OS. They still need fixing...

Addressed devices are not included in Collapse OS by default. Let's
just accept that upload only works with memory.

AGAIN, becomes a shortcut for "' RJMP AGAIN?,"

I decided to keep SKIP, .. TO, (renamed from AT,) around and limit
IF, .. THEN, to the simple BRNE case.

Will change to IF, .. THEN, but I need a way to easily reverse a
BR op. But from this commit, the translation of sms/kbd/ps2ctl.asm
is complete! perfect binary match!

Still making great progress on sms/kbd/ps2ctl. Still matching ref
binary.

next step: implement ST.

Getting good! still advancing on ps2ctl in sms/kbd and still
matching reference binary.