datalad-annex supports cloning from the web special remote,
using an url that contains the result of pushing to eg, a directory
special remote.

`datalad-annex::https://example.com?type=web&url={noquery}`

Supporting something like this in git-remote-annex would be good.

While to the user this might be considered part of the web special remote,
it would really be a separate download code path in git-remote-annex that
downloads from the urls.

datalad-annex assumes that the url uses the exporttree=yes layout.
If git-annex did the same, it would look in "$url/.git/annex/objects/".
But it could instead try both that and the regular hash directories
and use whichever it found.

How should the annex:: url look for this? It needs to contain the UUID of
the special remote (not the web special remote) because the MANIFEST key
includes the UUID. Perhaps "annex::https://example.com/?type=web&uuid=..."
or "annex::uuid?type=web&url=..." (in either case the inner url will need
to be URI-encoded)

What should be recorded in .git/config for such a remote? I suppose the
annex:: url and no annex-uuid. --[[Joey]]