my previous commit was only tested in emulation, I had init wrong.

Always returning zero caused test failures not to be properly
detected.

Although the SPI Relay driver is RC2014-specific, the SD Card driver
is generic enough to be a subsystem. That's the second subsystem we
add and this warrants, I think, the formalization of a new concept:
protocols.

It gives a better idea of where stuff can be moved/added to.

Among random "better safe than sorry" changes, the real fix is in
changing "4" for "5" above _find declaration. This off-by-one error
had that word, which is the root word in z80, have a 0x01 prev field
instead of a 0x00 one.

When all memory was initialized to zero, it didn't matter, we ended
up hitting 0 prev and considered ourselves properly at the end of
dict.

When memory wasn't initialized, however, we would end up jumping at
all kinds of places, leading to random behavior.

This should help spot bugs due to bad initialization.

The previous approach of maintaining R> and W> pointers was
conceptually simple, but made INT handler code actually quite
complex.

Now, we maintain indexes instead. It's much easier to perform
bounds checks and to compare for equality, something we have to
do quick in the INT handler.

it seems I left my asm argument harmonization half done here.

Instructions list at B208 doesn't correspond to many actual
mnemonics. This mnemonic here was the worst offender.

I've changed my mind about having documentation in-system. It doesn't
serve much of a purpose and make blkfs significantly heavier.

This commit is the first step in writing a documentation outside of
the blkfs.

Also, remove RSP underflow check from next for the same reason as
in the previous commit in z80.

with uflw checks not being in next anymore, we can save ourselves
a forward jump.

Also, remove underflow checks from next: it's taxing and useless
because underflow check already takes place in each relevant native
word.

They were a bit terse.

Under OpenBSD, stdin is already used by the device itself because of
the whole "stty has no memory" situation.

Previously, it could never write more than a few bytes before pingpong
getting a mismatch error. Now, I can pingpong Collapse OS binary
without a mismatch.

"-ansi" is not supported by tcc, but according to gcc
documentation, "-std=c89" produces identical behavior.

See: https://gcc.gnu.org/onlinedocs/gcc-3.4.2/gcc/Standards.html

It's a bit more inconvenient in terms of register protection (BC
is much more generally useful than IY), but it makes tight spots
such as next and execute much faster, so I think it's worth it.

The 1 byte limitation has been effective for a while now, but I
hadn't made the move yet, I wanted to see if the limitation would
cause me problems. It doesn't.

Doing this now slightly facilitates the IY->BC move in z80.

Bootstrapping: if you try to recreate the CVM binary from the
previous commit with this code, you'll have bootstrapping problems.
The first bootstrap will compile a binary with 2-bytes wide cells
but branching conditionals that yields 1-byte cells. That's bad.

I got around the issue by temporarily inserting a "397 399 LOADR"
instruction in cvm/xcomp.fs, right before the xcomp overrides. This
way, I force 1-byte cells everywhere on the first compiliation,
which then allows me to apply the logic change in cvm/vm.c and have
a properly running binary.

For the IY->BC move, of course.

In preparation for the IY->BC move

Bring native words together, make the next/exec/does/compiled
cluster be at the beginning.

Next step: bring find code into _find word.

I'm trying to move stuff around and it simplifies things. Will make
a lot more sense to inline when BC replaces IY.

This is in preparation of using BC instead of IY for IP. I've
verified all PUSH* usage and none was problematic.

There is now no more actual code in stable ABI, only references.
This makes refactoring of this code much easier. For example,
changing IY to BC as the IP register.

Only its jump addr remains.

This allows us to refer to pushRS/popRS routines by labels, allowing
us to get rid of the pushRS reference in the stable ABI zone.

Only its jump at 0x33 remains.

I've also fixed a strange offset oddity in 8086's (n) placement.
It was off by 2, but strangely, it ran properly. Anyway, now it's
fixed.