http://theory.stanford.edu/~amitp/GameProgramming/MapRepresentations.html#path-smoothing
http://aigamedev.com/open/tutorials/theta-star-any-angle-paths/
http://aigamedev.com/open/tutorial/lazy-theta-star/
http://www.aaai.org/ocs/index.php/AIIDE/AIIDE11/paper/download/4055/4436