I wanted to make CVM's forth use the Grid subsystem, but doing so
would break the stage binary. Hence, this split.

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

The C VM now runs the show.

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