Most of register fiddling routines (which is now the only thing contained
in care.asm) are used by almost all userspace apps, often in inner loops.
That makes the penalty of using jump tables for those a bit too high.
Moreover, it burdens jump tables needlessly.
Because this unit is very small (now that string routines are out), it makes
sense to always include it in binaries.
The goal is to avoid mixing those routines with "character devices"
(acia, vpd, kbd) which aren't block devices and have routines that
have different expectations.
This is a first step to fixing #64.
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.
