code: func (d *Document) GunningFog() float64 {
  	x := d.NumWords / d.NumSentences
  	y := d.NumComplexWords / d.NumWords
  	return 0.4 * (x + 100.0*y)
  }
docs: // GunningFog computes the Gunning Fog index score
  // (https://en.wikipedia.org/wiki/Gunning_fog_index).