code: func StdDev(floats []float64) float64 {
  	var sum float64
  	a := Average(floats)
  	for _, f := range floats {
  		sum += math.Pow(f-a, 2)
  	}
  	return math.Sqrt(sum / float64(len(floats)))
  }
docs: // StdDev returns the standard deviation of a random variable