code: func (f *FileStats) StatLine(previous *FileStats, span time.Duration) string {
  	var bytesDownloaded uint64
  	if previous != nil {
  		bytesDownloaded = f.BytesCompleted - previous.BytesCompleted
  	}
  
  	return fmt.Sprintf("Files (%d/%d) - %s / %s - %0.1f%% - %s/s",
  		f.CountCompleted, f.CountScheduled,
  		humanize.Bytes(f.BytesCompleted), humanize.Bytes(f.BytesScheduled),
  		100*float64(f.BytesCompleted)/float64(f.BytesScheduled),
  		humanize.Bytes(uint64(float64(bytesDownloaded)/span.Seconds())),
  	)
  }
docs: // StatLine calculates a simple statistics line suitable for logging.