World builder now loads the tile map json and usese the keys to figure out how to randomize the floor configurations.

tilemap.hpp

@@ -40,6 +40,7 @@ public:
   void load(matrix::Matrix &walls);
   const TileCell &at(size_t x, size_t y);
   void set_tile(size_t x, size_t y, std::string tile_name);
+  std::vector<std::string> tile_names();
 
   void dump(int show_x=-1, int show_y=-1);
   bool INVARIANT();