Add parent / child with blue & green in order to enter / exit from a building. Example: ```json { "world": 1, "back": "assets/worlds/player_house/ph1_back.png", "front": "assets/worlds/player_house/ph1_front.png", "collision": "assets/worlds/player_house/ph1_col.png", "building": true, "city": 0, "enter": {"x": 0, "y": 0}, "exit": {"x": 0, "y": 0} }, ```
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