-- you should be able to restore without setting up a config file.
   if you lost data, that'd be annoying.  restoring from a config
   file will be supported in the future, but it's not yet.

-- backups must be automatable, never requiring user input. hence public
   key encryption.

-- restores may prompt for user input ("What's your Amazon S3
   password?" and "Enter your GPG passphrase."), because they won't be
   automated or common. and I don't want a restore to require a fully
   setup ~/.brackup.conf. You probably lost it anyway. So a *.brackup
   metafile (the one you get after a backup) should contain all the
   metadata necessary to restore (say, Amazon S3 username), but not
   secret stuff.

-- targets shouldn't include passwords (say, Amazon S3 password)
   in the *.brackup (backup "index"/"meta" file).  let the user
   enter that on restore.  you should, however, put in metadata
   that'll ease restoring.... like Amazon username, or path, etc.