[Borgbackup] Some prototype features

[Thomas Levine]

Borg lacks many features in fossil that I really like, so I have written
rough equivalents of my favorites for my own use. Has someone already
written them better? The important features are

* Configuration of repository access settings with ``torg open`` and
``.trgckout``
* Using settings from a checkout-specific file instead of from the shell
arguments
* Run commands on all repositories with ``torg all``, like in ``fossil
all``

If not, maybe they can at least inspire something. If repository
settings are stored more formally, we can have things like a
checkout-specific default compression and global default excludes file.
Then creating an archive could be even shorter than it already is, like
just "borg create name-of-archive" (inspired by "fossil commit -m
commit-message"). And if checkouts and repositories are indexed
centrally, we can easily run commands on all of them at once.

I use fossil for versioning of small things and borg for versioning of
everything else. With the two features above, my backup procedure gets
much easier. First I append new commits in the fossil repositories to
their remotes.

$ fossil all push

Then I create new borg archives and append them to their remotes.

$ torg all create ARCHIVE-NAME

My implementation is here.
https://thomaslevine.com/scm/torg/artifact/8580af67aee9b738