docs: def center (self):
      """center() -> (x, y)
  
      Returns the center (of mass) point of this Polygon.
  
      See http://en.wikipedia.org/wiki/Polygon
  
      Examples:
  
      >>> p = Polygon()
      >>> p.vertices = [ Point(3, 8), Point(6, 4), Point(0, 3) ]
      >>> p.center()
      Point(2.89285714286, 4.82142857143)
      """
      Cx    = 0.0
      Cy    = 0.0
      denom = 6.0 * self.area()
  
      for segment in self.segments():
        x   = (segment.p.x + segment.q.x)
        y   = (segment.p.y + segment.q.y)
        xy  = (segment.p.x * segment.q.y) - (segment.q.x * segment.p.y)
        Cx += (x * xy)
        Cy += (y * xy)
  
      Cx /= denom
      Cy /= denom
  
      return Point(Cx, Cy)