code: func sloper(x1, y1, x2, y2 int) (m, r float64) {
  	dy := float64(y1 - y2)
  	dx := float64(x1 - x2)
  	m = dy / dx
  	r = math.Atan2(dy, dx) * (180 / math.Pi)
  	return m, r
  }
docs: // sloper computes the slope and r of a line