iOS内购后台监订阅回调

接触新编程时，无论它看起来和之前的多么相似，简单处理或许没问题，要是处理得当完美，最好是拉到有经验的同事一起来讨论，向他学习！细节决定成败

https://cloud.tencent.com/developer/article/1445964

http://www.cocoachina.com/cms/wap.php?action=article&id=25323

https://www.jianshu.com/p/abd2ba4deb54