Recipes contain bits and pieces of hardware-related knowledge, but
these bits feel sparse. I've been wanting to consolidate hardware-
related documentation for a while, but always fell at odds with the
recipes organisation.

We don't have recipes anymore, just a /doc/hw section that contains
hardware-related documentation which often translate to precise
instructions to run Collapse OS on a specific machine.

With this new organisation, I hope to end up with a better, more
solid documentation.

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's more descriptive this way. Also, I'll soon add a new HERESTART
config.

Driver configuration don't need their own words at runtime, we only
need to compile them as literals when compiling words.

Now that we have this "declaration blocks" pattern emerging, it
seems like a good idea to take advantage of this in drivers, both
for simplifying the xcomp unit and to make final binary slimmer.

This was becoming heavy to manage.

This is the first commit I do entirely in VE. It's a habit I'm planning
on taking as it helps a lot to find usability issues.

And use them in all places they make sense.

This would allow things like temporary giving control to the *CL
line on the TRS-80. For example... A very far fetched example. Not
at all the only *raison d'etre* of the layer...

We can get rid of acia.z80, but not of acia.fs yet, we still need it.