docs: def new_percent_saved(report_stats):
      """Spit out how much space the optimization saved."""
      size_in = report_stats.bytes_in
      if size_in > 0:
          size_out = report_stats.bytes_out
          ratio = size_out / size_in
          kb_saved = _humanize_bytes(size_in - size_out)
      else:
          ratio = 0
          kb_saved = 0
      percent_saved = (1 - ratio) * 100
  
      result = '{:.{prec}f}% ({})'.format(percent_saved, kb_saved, prec=2)
      return result