SCS2

[Markus Demleitner]

Dear DAL folks,

I have procrastinated my College Park homework for a bit too long
already, but now I just have to carve out some time for it: Cone
Search 2.

The main purpose of this will be to test strategies for major version
transitions, but it is also a nice opportunity to explore how to
opimally re-use what we already have in DALI, and of course SCS2
itself should be (slight) progress over SCS1, too.

I have just pushed a first commit drafting out the protocol itself,
remaining as close to SCS1 (in concept) as possible (but not actually
re-using significant amounts of texts):
<https://github.com/msdemlei/scs2>.

I am planning to write, over the next few weeks, sections on:

* Registry aspects (stressing the importance of tablesets, also
  mentioning the possibility of having auxiliary SCS capabilities)
* Appendix A: Non-normative recommendations for clients
* Appendix B: A transition plan

Until that's done, I plan to not move this into ivoa-std und directly
commit to main.  You'd be welcome to do the same; let me know and
I'll add you as a collaborator.

Once the basic text is there, I will of course move to ivoa-std and
follow its rules.

Still, even at this stage, collaborators and reviewers are most
welcome.

Thanks,

          Markus