Working in "blk/" folder from a modern system is harder than it
should be. Moving blocks around is a bit awkward, grepping is a
bit less convenient than it could be, git blame has troubles
following, etc.

In this commit, we modify blkpack and blkunpack to work with single
text files with blocks being separated by a special markup.

I think this will make the code significantly more convenient to
work into.

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.

I'm about to reuse sdc.c in sms.c and the old directory structure
was becoming awkward.

I'm planning on adding other subfolders. 8086 for example...

Running a ROM on an everdrive is one thing, but running a ROM
directly is another: my hacked up sega.bin didn't have a proper
checksum, so the ROM didn't run.

This new tool transforms a binary into a properly-headered ROM.

Has been tested on an actual SMS.

Much faster!

All recipe makesfiles would previously assume a built emul/.

Fixes #113

This allows us to get rid of the zasm.sh wrapper.

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.

This makes for a much more usable zasm linux binary that doesn't have to
be rebuilt every time apps or kernel change.

... instead of embedding it in the binary itself. Additionally, add a
"zasm.sh" wrapper to faciliate zasm calls on a linux machine.

Also, clarify the role of recipes.