Android: 如何实现 in_app purchase

日后补全：

参考资料：

http://developer.android.com/guide/market/billing/index.html

http://stackoverflow.com/questions/2022945/implementing-in-app-purchases-in-android

http://stackoverflow.com/questions/5696960/in-app-billing-tutorial/6292728#6292728

http://blog.blundell-apps.com/simple-inapp-billing-payment/