Makes xcomp.fs units shorter.

TODO: implement X['] so that I can remove those XCURRENT patterns.

This leaves space for xcomp-core which is growing.

This allows us to move words like ABORT" to xcomp-core, which is
I think the last roadblock before being able to unify all drivers
into a single xcomp layer.

Now I struggle to remember why I ever did things they way I did.
There must have been a reason...

The goal is to insert device drivers in between.

I'd like to move this code, along with all recipe contents, to blk/.
It's easier if "emul-related" code is gathered at the same place.

With all this recent movements, we had a bit of a fragmentation
issue.

I'm reserving the 100-200 range for non-bootstrapping needs.

no floppy yet.

Not much of a gain in terms of usability (a bit of a loss in fact, things are
a bit slow and glitchy), but it's a necessary move if we want to use upcoming
grid-enabled userspace apps, such as a visual text editor.

This allows us to write contents from RS-232 directly to floppy! it works!

Sending the escape after its target made things complicated for upcoming
stuff I want to add. Although it makes `recv.asm` slightly larger, it's really
worth it.

Read-only support for now, hardcoded on drive :1. But it seems to work.

Can't wait to get a CFS running on this!

Lines should be terminated only with a CR on this system, not CRLF.