Fixed the game crash on unfound sound resource
pathfinding: beautifications of code

opengl block indent, this-> ptrs
datastructure/pairing_heap: 100% test coverage and functionality
pathfinding: relocated coordinate hashing to std namespace
datastructure/pairing_heap: created type member for heap nodes
pathfinding: utilize std::hash<coord::phys3> in nodemap
pathfinding: remove hardcoding for navigation grid size

now using 1/8 of the phys-resolution per game tile
pathfinding: moved cost comparison from a_star to path

this also fixes using the correct operator for the pairing heap:
< instead of >
pathfinding: use pairing_heap instead of std::priority_queue
pathfinding: code beautifications and comments
Merge pull request #168 from TheJJ/pairing-heap

Use pairing heap in pathfinding
pathfinding/path: removed unused includes
Merge pull request #147 from jprashanth/sounds-loc

Look for sound files in both sounds.drs and sounds_x1.drs folders
Merge remote-tracking branch 'upstream/master' into arrows_fired

Conflicts:
	cpp/game_main.cpp
	cpp/unit/ability.cpp