fixes #80

Also made Makefile actually portable.

It's no longer required to use `gmake` under OpenBSD and shell scripts
no longer require bash.

Also, add the new `bshell` emulated tool. BASIC is on its way to replace the
shell.

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.

Let's see where it will lead us...

This way, we can compile apps from within the shell that run on the
shell.

What used to be `tools/emul/user.h` was in fact specific to zasm, so I
moved it there.

To avoid name confusion, I renamed what used to be kernel.h and user.h
to kernel-bin.h and user-bin.h.

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

The next step is to generate them on-the-fly.

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

It was a bad idea to remove it. Now that I'm introducing the concept of
a per-app glue file, it becomes much easier to build emulated zasm as a
userspace app.

Let go of that "meta os" thing. it's not as meta as I made it sound
like. It's a kernel.

Made things complicated for nothing.

To straighten out includes and to pave the way into zasm being part of
the same "include CFS" as parts, we make zasm includes namespaced.

This shrinks the CFS size to 21k from nearly 64K. This will allow me to
kick the can down the road a bit with regards to supporting storage
seek/tell greater than 64K.

I'll get to it, but first, I want to assemble zasm with zasm!

Will be much much easier to tests new core routines without having to
re-create their context first.

Also, extract parse.asm from core.asm

On build, pack `parts/z80` into a CFS and embed it into the emulated
zasm executable as an fsdev. This will allow for the upcoming include
directive to have something to go to.

For now, this is useless except for inflating the emulated zasm's size.

With the help of the newly-introduced cfspack tool, we can mount a
filesystem in our emulated shell and play around. Read-only for now.
Unpacking incoming.