ASTStoreKit 介绍
ASTStoreKit 用来 appstore 上应用常用的一些方法，包括：
- Built-in and fully functional store view controller
- Configurable using plist files (no code changes required to the library itself)
- Supports consumable, nonconsumables, and autorenewables
- Supports consumable families to enable multiple product ids to manipulate the same resource
- Delegate methods for all of the major changes you might want to be notified about
- Ability to wipe local data clean (for debug and for dealing with possible corruption)
- Testing in simulator using the embedded SimStoreKit (not including AutoRenewables)
- Encrypted family data storage for purchase quantities