ref #80

fixes #80

Also made Makefile actually portable.

markdown formatting was broken. Also, don't mark it as WIP.

This shaves off quite a few bytes from the binary.

This is becoming the new shell, it has to step up to its new responsibilities!

Shell replacement sequence beginning in 3, 2, 1...

Mechanism for assigning inputs to the specified variable is clumsy and uses
binary space. Always using A is much simpler and doesn't seem very limiting to
me. I do that because there's many more "input" commands I'd like to add.

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

Also, fixed the cmd matching algo to not accept partial matches. For example,
to stop matching "input" when the command was "in".

also fix broken "peek"

It's an awkward register to use and avoiding its use allows us to strip the
resulting binary significantly. parseEXPR keeps the same signature though.

Things are getting super cereal...

Things are getting cereal...

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...