Add basic sqaure grid heuristic functions.

alib2graph_algo/src/heuristic/ChebyshevDistance.cpp

alib2graph_algo/src/heuristic/ChebyshevDistance.hpp

alib2graph_algo/src/heuristic/DiagonalDistance.cpp

alib2graph_algo/src/heuristic/DiagonalDistance.hpp

alib2graph_algo/src/heuristic/EuclideanDistance.cpp

alib2graph_algo/src/heuristic/EuclideanDistance.hpp

alib2graph_algo/src/heuristic/EuclideanDistanceNoSQRT.cpp

alib2graph_algo/src/heuristic/EuclideanDistanceNoSQRT.hpp

alib2graph_algo/src/heuristic/ManhattenDistance.cpp

alib2graph_algo/src/heuristic/ManhattenDistance.hpp

alib2graph_algo/src/heuristic/SquareGridHeuristics.hpp