Unit tests for pathfinder

[wheybags]

Unit tests are defined here: https://github.com/wheybags/freeablo/blob/master/test/CMakeLists.txt#L31
Pathfinder code is here: https://github.com/wheybags/freeablo/blob/master/apps/freeablo/faworld/findpath.cpp
Pathfinder manual testing executable is here: https://github.com/wheybags/freeablo/blob/master/apps/findpath/main.cpp