No.8 for 224e054d

Code-Change & finish the figure-moving animation.

Code-Review & some comments
  1. Added some comments in the game model, explaining what's being done
  in the functions, mostly for my own convenience.

  2. Using a currentVector to replace currentDirection+moveVector. This
  is to support the moving between disconnected sections.

  3. Removed the last point in checkPoints list, as that will cause ugly
  effects when the goal is reached. Now the last point is the last
  checkpoint in section 'Y'.