Also, make parseHexadecimal "tail" (HL). Soon, all routines in lib/parse
will do that, making the life of lib/expr easier.

This unit is being removed.

Finally getting rid of this bad mistake of using IX for this.

Those replacements were trivially equivalent. For the other ones, an
examination of the context is necessary.

This completes instruction support for the Blink tn45 example.

Take argspec pairs directly as an argument instead of taking a
pointer to an argspec pair.

The instruction table is now beefier and has redundant data, but
this simplifies processing. This should simplify upcoming work.

Also, add a "real world" example in AVRA tests, a blink program on
a ATtiny45. Some instructions are commented out because they aren't
implemented yet, but not many.

The output of the program has been verified against AVRA's own
output.

This costs us a bit of space for now but should make things a lot
simpler down the road, especially with "alias ops" which are simple
syntactic sugar for another op.

I had written this when trying different approaches to adding BR and
I forgot to remove it.

Use IX directly for argspec rows instead of going through DE. It saves a bit
of processing. The code was this way because I initially didn't use IX at all,
so as code evolved, that DE translation stayed as an artifact.

It wasn't used much so I inlined it.

Again, same thing as in zasm.

Same thing as in zasm.

It can only print a decimal literal. But still, that's a big step because
I hadn't implemented decimal formatting yet.

That's my mega-commit you've all been waiting for.

The code for the shell share more routines with userspace apps than with kernel
units, because, well, its behavior is that of a userspace app, not a device
driver.

This created a weird situation with libraries and jump tables. Some routine
belonging to the `kernel/` directory felt weird there.

And then comes `apps/basic`, which will likely share even more code with the
shell. I was seeing myself creating huge jump tables to reuse code from the
shell. It didn't feel right.

Moreover, we'll probably want basic-like apps to optionnally replace the shell.

So here I am with this huge change in the project structure. I didn't test all
recipes on hardware yet, I will do later. I might have broken some...

But now, the structure feels better and the line between what belongs to
`kernel` and what belongs to `apps` feels clearer.

Instead of expecting a `USER_CODE` symbol to be set, we expect `.org` to be
set in all userspace glue code. This gives us more flexibility with regards to
how we manage that.

Moreover, instead of making `USER_RAMSTART` mandatory, we make it default to
the end of the binary, which is adequate in a majority of cases.

Will be useful for my upcoming mega-commit... :)

Also important for upcoming mega commit...

Will be important for a mega-commit I'm preparing.

Most of register fiddling routines (which is now the only thing contained
in care.asm) are used by almost all userspace apps, often in inner loops.

That makes the penalty of using jump tables for those a bit too high.
Moreover, it burdens jump tables needlessly.

Because this unit is very small (now that string routines are out), it makes
sense to always include it in binaries.

Can possibly avoid a lot of debugging pain.

Also, make empty strings be parsed as invalid by parseDecimal.