Restic: Add a 'verbose' log level that logs just what happened

The new restic 0.9.0 has improved logging with four levels of detail:

1. --quiet -> nothing (except errors)
2. just completion stats
3. --verbose or -v -> major steps and completion stats
4. --verbose --verbose or or -v 2 -> major steps, all files, completion stats

However, none of these level logs just what files got backed up. Just -v doesn't log files, and -v -v logs every file even those that are not being backed up (unmodified).

My suggestion was to add a level that logs just what happens during the run, ie. files that are added, modified, or deleted in this snapshot, e.g.

1. --quiet -> nothing (except errors)
2. just completion stats
3. --verbose or -v -> major steps and completion stats
4. --verbose --verbose or or -v 2 -> major steps, added/modified/deleted files completion stats
5. --verbose --verbose --verbose or or -v 3 -> major steps, all files, completion stats

Alternatively log feature labels could be used, to turn options on/off, e.g.

--log=scan,added,modified,deleted,unmodified,totals,stats

And so just to log files backed up with no totals at the end you could use

--log=added,modified,deleted

If you just want totals, you could use

--log=totals

And the --verbose options would map to some preset combinations of log features.

The stats option would enable details per-file stats, with total file size and size actually backed up, and upload times.