A* algorithm and data structures started

Created AStareNode to be used by the A* algorithm with an easy access to
previous calculations. Started to implement the basic A* algorithm.
Removed compile error
Merge branch 'master' of https://github.com/milseman/sokoban.git
A* finished
Merge branch 'master' of https://github.com/milseman/sokoban.git
Merge branch 'master' of https://github.com/milseman/sokoban.git
Finished Manhattan huristic and A* in basic form