Social Web Protocols update

Hi everyone,

I've (finally) done a major overhaul of Social Web Protocols
<http://w3c-social.github.io/social-web-protocols/>. As the WG is producing
multiple specs which in some cases overlap functionality, this document
explains how to map your requirements to the right spec. Specs are compared
side by side, broken up by the functions they perform. There's also a
summary table at the top.

There are still some very-draft or unfinished sections for areas that came
through the use cases / requirements gathering but which haven't been
addressed in depth by the WG yet. Hopefully we'll get to talk about some of
these at the face-to-face.

I'd appreciate it if you can read it through, as I'd like to agree to
update the WD during the next call on Tuesday.

As ever, if I've missed something or made glaring errors or minor typos,
issues and PRs are welcome. I particularly welcome input from the editors
of the specs discussed, as you're the most likely to spot if I've
misunderstood something :)

Thanks!

Amy