message: Add 3D MapCoordinate accessor to Tile
diff: @@ -39,8 +39,8 @@ public:
  TerrainType index() const { return mIndex; }
  void index(TerrainType index) { mIndex = index; }
  + const MapCoordinate& xyz() const { return mPosition; }
  NAS2D::Point<int> xy() const { return mPosition.xy; }
  -
  int depth() const { return mPosition.z; }
  void depth(int i) { mPosition.z = i; }
  