The 🐑 Shepherd gets a service collection

["Ludovic Courtès" <ludo@gnu.org>]

Hello Guix!

I pushed some changes yesterday that confirm that the Shepherd paves the
way for init system innovation, synergistic cross-domain fertilization,
and delimited continuations:

  https://git.savannah.gnu.org/cgit/shepherd.git/log/?id=31d21fa083872d500c016b6b3b2587d25510702d

  31d21fa * Add REPL service.
  cd6f3fb * comm: Add 'open-server-socket'.
  c64804f * Add resource monitoring service.

These new services are built into shepherd, allowing users to control it
and to fiddle with it.  The REPL is functional but of course a bit
bumpy: you’d better know what you’re doing.

I imagine we could develop more convenient services like this, such as a
basic command scheduler similar to the ‘at’ command, and a syslogd
implementation.  The latter could be nice for a couple of reasons:
logging would happen from the start and till the end (an improvement
over the external syslogd process), and it could let us provide a nicer
user interface to view logs (taking inspiration from that of
‘journalctl’).

Thoughts?  Ideas?

Ludo’.

PS: It just occurred to me that we might as well rename the new
    (shepherd service …) hierarchy to (shepherd sheep …) or even
    (shepherd 🐑 …).