"Improve logging"

Logging does not seem useful currently (from a user point of view). It would be great to have logging that is useful to us end users.

Here is a brainstorming proposal (inspired by rsync)

> kopia --log-level=help

BACKUP     Mention files backed up
MOUNT      Mention mounts that were found or skipped
SKIP       Mention files that are skipped due to ignore rules
STATS      Mention statistics at end of run (including compression)
DEBUG      Mention debug info for developers
CACHE      Mention cache entries
WARN       Mention warning
ERROR      Mention errors

ALL        Set all --info options
NONE       Silence all --info options
HELP       Output this help message

> kopia snapshot create /path/to/folder --log-level=skip,stats,warn,error

There is some progress. Please see also