The dual scraptchpad thing doesn't work. Things become very
complicated when it's time to write that back to the file. We
overwrite our contents and end up with garbage.

This hard-binds ed to the filesystem (I liked the idea of working
only with blockdevs though...), but this is necessary for the
upcoming `w` command. We need some kind of way to tell the
destination to write to truncate itself.

This only has a meaning in the filesystem, but it's necessary to
let the file know that its registered file size has possibly
shrunk.

I thought of alternatives that would have allowed me to keep ed
blkdev-centered, but they were all too hackish to my own taste.

Hence, this new hard-bind on files.

During expression parsing, if a local label was parsed, it would
select the local registry and keep that selection, making
subsequent global labels register in the wrong place.

I'm about to break compatibility with scas. Before I do that, I
need to adjusts tests. Instead of running scas to compare results,
we commit expected result as binaries directly in the repo.

Looping inside ReadC broke the shell's hook logic. We have to
return immediately when nothing is typed.

Also, make tests run in a *BSD environment

It was mostly wrong.

Sure, it's a bit slower, but it prevents a lot of hard to debug
problems. I don't have to want to remember "don't use IX if you
have any blk* calls". Let's optimize I/O later.

Starting to feel interactive...

A routine to conveniently read lines from TTY. Extracted from
shell. Will be used in other places.

That is, send current chr selection, and then, send LF.

This avoids having "ghost" chr selection sticking around.

This allows for outputting a character selection before it's given
through GetC. That allows a pad-oriented character selection scheme.

Still a bit rough around the edges, but still, works rather well.

This hook is called during every iteration, allowing regular screen
refresh when video is involved.

Now this is getting eminently exciting!