This will facilitate the development of a solution for
cross-compiling directly to EEPROM.

NetBSD doesn't have ncurses. Linking to curses doesn't seem to change
anything. Tried on OpenBSD and Ubuntu.

It works (in emulation, but soon on real hardware!), but the LIST
command is awkward due to tight screen estate...

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...

libz80 doesn't move much anymore, there not much advantage to the
git module indirection.

This will allow us to implement AT-XY, paving the way to all sorts
of nice new things.

It doesn't change anything featurewise, but this change is in
preparation for the addition of an eventual AT-XY.

It's not used

To update LATEST offset more easily. Will be useful for recipes.

This requires us to significantly adjust our build process, which
now has 3 stages.

fixes #80

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

fixes #79