code: func (m *monitor) harvest(ref string) ([]string, reddit.Harvest, error) {
  	h, err := m.scanner.Listing(m.path, ref)
  	return m.sorter.Sort(h), h, err
  }
docs: // harvest fetches from the listing any posts after the given reference post,
  // and returns those posts and a reverse chronologically sorted list of their
  // names.