We now have a stable ABI that is pretty cleared up...

The only calls still using the stable ABI indirection are those
made before the next routine is created.

Instead of having wordref point to core word routines, I made them
into word 4 word types. It liberates space into the stable ABI and
should make porting to other arches easier.

I'm also thinking of combining word type with the namelen field
for precious bytes saving, but not now...

It was useful when we still had the relinker, but now it has no use.
I was waiting a bit to see if the distinction would be useful again,
but it seems like it won't.

Only 2>R in actually needed in the RSP family (for LOOP). Reducing
the scope of the stable ABI makes porting to other arches easier.

I had more ambitious goals, but I backed out of it: not worth it.
This small optimization is an easy picking though.

Inline it in next and make chkPS, call a newly reserved label for
it directly, removing a layer of indirection. This frees a spot in
the stable ABI.

Otherwise, when editing a file with VE, we would constantly write
to disk, which is a bit inefficient.

It's a quite useful word and it doesn't make sense to reload it from
disk after each usage.

All recipe makesfiles would previously assume a built emul/.

Fixes #113

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.

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.