FIXME
 ☐ robustness: do not allow 'use repo' to write file, when repo is not valid

TODO
 ☐ command 'set_defaults repo' - sets all valid attributes to some sensible value
   ☐ set user's login name as username
   ☐ generate password for serving directories

MAYBE
 ☐ specialized copy commands:
   ☐ copy without dependencies
   ☐ copy sdists only, not wheels
   ☐ copy packages listed in a requirements.txt file
   ☐ copy all versions of package(?)
   ☐ copy all packages in repo
 ☐ command 'clean repo' - remove all extra attributes
