code: function(lst, x, y, w, h) {
        lst.push(new Wall(new Vec(x,y), new Vec(x+w,y)));
        lst.push(new Wall(new Vec(x+w,y), new Vec(x+w,y+h)));
        lst.push(new Wall(new Vec(x+w,y+h), new Vec(x,y+h)));
        lst.push(new Wall(new Vec(x,y+h), new Vec(x,y)));
      }
docs: World object contains many agents and walls and food and stuff