text: Title: Should check linkage ground contact in reverse order 
  Body: https://github.com/mithi/hexapod-robot-simulator/blob/f67434e8a3c8bd8e0dfaa73631b2050a24530c01/hexapod/linkage.py#L161
  
  IE do this instead
  ```python
          ground_contact = self.p3
          for point in reversed(self.all_points):
              if point.z < ground_contact.z:
                  ground_contact = point
  ```