+/* Add thing of "id" and "type" to map on random passable position (positions
+ * which contain an actor are not deemed passable) if "find_pos", else on y=0,
+ * x=0. If "id" is >= 0 and <= UINT8_MAX, use lowest unused id. Return thing.
+ */
+extern struct Thing * add_thing(int16_t id, uint8_t type, uint8_t find_pos);
+