It's been a long while since I visited this part of the code and it
has become a bit messy after having gone through all evolutions of
the core code.

It is now simpler, more compact.

Previously, these words would be ascii emitters, but seldom used
except for the SPC emitter. However, I would often end up hardcoding
these constants. With useless emitters removed and ASCII constants
added, we have a more usable system.

Also, fix broken test harness.

It doesn't require emitting words anymore. The rename to NL> is
linked to the upcoming commit.

... and rename it to KEY?. Then, add KEY from KEY? for its blocking
version.

I need this for an upcoming Remote Shell feature. If a Collapse OS
system remotely controls another shell, it needs to be able to poll
both the remote system and the local keyboard at the same time. A
blocking KEY is incompatible with this.

In some places, the polling mechanism doesn't make sense, so this
new KEY? always returns a character. In some places, I just haven't
implemented the mechanism yet, so I kept the old blocking code and
added a "always 1" flag as a temporary shim.

I have probably broken something, but in emulators, Collapse OS runs
fine. It's an important reminder of what will be lost with the new
"dogfooding" approach (see recent mailing list message): without
emulators, it's much harder to to sweeping changes like this without
breaking stuff.

It's fine, I don't expect many more of these core changes to the
system. It's nearly feature-complete.

Also, turn AT28! and AT28, into ~AT28, pluggable into ~C!.

~AT28 doesn't check for mismatches. It was too complicated to turn
a mismatch into a compiled word we would jump to next. Data
integrity has to be checked through another path.

Also, remove MOVEW. Without indirect memory access, this word
doesn't make sense. Some AVR-specific words will have to be
defined.

I got bitten again, I've over-designed my solution. The last time
it happened, it was that memory mapping thing I was wanting to add.

The indirect memory access feature I was adding was to solve a
specific problem: Allow Collapse OS to cross-compile directly on a
AT28 EEPROM.

It began well. As long as we were staying in the assembler realm,
things were looking good. However, when we got into the xcomp realm
(B260), things became ugly, and I had to creep up indirection where
I didn't want to.

All of this because I wanted to solve my initial problem in a
slightly more generalized way. The broad idea was that these indirect
memory access could allow xcomp into a broad kind of memory-like
devices.

This idea broke on the "@" part of the equation. If I want
indirections to be two-way and allow xcomp to work properly, I have
to add this indirection to FIND (and possibly others) and this just
isn't practical or elegant.

So, I'm taking a step back and accepting that the solution I design
for now is exclusively for the AT28. What I'm thinking is to add a
low-level hook for memory writing, at the assembly level.

Splitting a word into MSB/LSB pairs happens often and is worth, I
think, native words. Also, I'm going to need it in the upcoming
commits.

Also, rename "Addressed devices" to "Indirect memory access".

I do this because I need to add indirect versions of !, @ and ,
to allow boostrapping directly to EEPROM and that A,, thing I've
added to assemblers felt like really bad names.

With this change, I'd like to generalize the use of the * suffix
for aliases.

This brings us a bit closer to TYPE from Forth 2012. I don't think
I'll add TYPE (sig "addr len") anytime soon because there is few
use cases for it, but having "STYPE" instead of "(print)" feels
cleaner.

The switch name was confusing.

It isn't used in there anymore. Moved it to VE, the only place
where it's used.

There are many situations where it can be useful. Worth it.

This allows us to remove AMOVE* words.

I'm pretty happy about how lightweight the implementation turns
out to be.

They were only used in the ti84 recipe and were not worth their cost.

Adding a delay such as the 20ms one we have in AVR programmer's
initialization routine is tricky without a word like TICKS.

This implementation is highly inaccurate, but more accurate and
reliable than a "ballpark" DO..LOOP...

The ":" now takes care of scanning for ";". Conceptually, having
";" as an immediate word is slightly simpler than the approach in
this commit, but when bootstrapping is involved, this simpler
approach gets murkier.

Moreover, it got even murkier-er when trying to de-stabilize EXIT,
so here we are.

This duplicated feature existed because of bootstrapping issues
with LIT", but again, with careful threading, we can clean things
up.

We can now have a proper "Collapse OS" prompt :)