VOSI: removing availability

[Markus Demleitner]

Dear DAL, Dear GWS,

[I'd suggest followups to GWS]

Pat and I have moved the VOSI sources to github,
<https://github.com/ivoa-std/VOSI>.  

The reason I am in this is because of the decision passed at the last
Interop to no longer require availability endpoints (background:
<https://ivoa.net/documents/caproles/>. In the interest of reducing
the number of bells and whistles that VO implementors may feel
obliged to implement, I'm suggesting to remove (almost) the entire
spec of Availability (see below) in VOSI PR 1
<https://github.com/ivoa-std/VOSI/pull/1>.  I'd much appreciate
comments on this; in particular, we might decide to just make it
optional instead, although I'd then ask about actual use cases for
burdening an interoperability spec with it.

Into the PR I'm also sneaking in a few Todos I noticed while scanning
the document for text to change.  I'd say a separate PR for that
would be overdone bureaucracy, but I'll make one if people are
actually concerned by the two-topic PR.  Or, yikes, turn them into
Github PRs, although I'd much rather have them in the interoperable
git history than in the proprietary github issues, to be frank.

Which brings me to the next question: Who'll serve as editor for this
round of VOSI?

Since I really would like to somehow resolve the situation that we
require availability endpoints for all of our services, but only 367
of 24804 actually have one (and, even worse, nobody bothers and the
VO just runs fine with almost everyone violating this requirement),
I'd volunteer for the availability change (even if it were to mutate
into just making it optional) and the todos I've put in.

But then I think the standard would profit from a bit more polishing,
in particular smoothing out a few more SOAPisms that still are in
there, and that I'm not volunteering for.  Plus, I'd much rather not
be editor here.  So... if anyone else could see themselves serving as
editor, I'll be really grateful (and already promise buying this
editor a $BEVERAGE when there'll be proper interops again).

Thanks,

            Markus