add area destroy function

obj/Area.lua

@@ -32,6 +32,18 @@ function Area:draw()
     for _, game_object in ipairs(self.game_objects) do game_object:draw() end
 end
 
+---Destroys area
+function Area:destroy()
+    for i = #self.game_objects, 1, -1 do
+        local game_object = self.game_objects[i]
+        game_object:kill()
+        table.remove(self.game_objects, i)
+    end
+    self.game_objects = {}
+
+    if self.world then self.world = nil end
+end
+
 ---Adds game object to area
 ---@param game_object_type string name of game object's class
 ---@param x number|nil horizontal position