code: func (l *Line) Bound() *Bound {
  	return NewBound(math.Max(l.a[0], l.b[0]), math.Min(l.a[0], l.b[0]),
  		math.Max(l.a[1], l.b[1]), math.Min(l.a[1], l.b[1]))
  }
docs: // Bound returns a bound around the line. Simply uses rectangular coordinates.