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.

Sub-parsers are seldom used by themselves, except for parseDecimal.
I'm tightening the code of this unit for two reasons:

1. Optimization
2. Upcoming API change where HL won't be preserved anymore, but will
   point to char following the last parse char. This will allow us
   to simplify lib/expr.

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

Instead of going left and right, finding operators chars and replacing them
with nulls, we parse expressions in a more orderly manner, one chunk at a
time. I think it qualifies as "recursive descent", but I'm not sure.

This allows us to preserve the string we parse and should also make the
implementation of parens much easier.

For some reason, I've mistakenly disabled tests in test_expr without noticing
and I also broke "-123" parsing. Fixed.

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

This should make tests a bit more convenient to write and debug.

Moreover, begin de de-IX-ization of parseExpr. I have, in a local WIP, a
parseExpr implemented using a recursive descent algo, it passes all tests, but
it unfortunately assembles a faulty zasm. I have to find the expressions that
it doesn't parse properly.

But before I do that, I prefer to commit these significant improvements I've
been making to tests harness in parallel of this development.

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.

We now treat the block device as fixed-size rather than trying to grow it in response
to kernel activity.

Previously, if you tried to create 2 files in a row, only the first 1 would actually appear,
because the device only ever got larger when a byte was written immediately past the end of
the device.

Now we just let the kernel write bytes to the disk anywhere, so new files can be created even
when the previous file is not completely full.

Also, fix buffer overrun in reading filesystem image, and use a more idiomatic fgetc loop.

It wasn't used much, so I replaced its use in the kernel with direct code
and moved the routine in apps/ed, the only other place where it was used.