ASHUIAlertView

可直接调用这个方法，直接使用block代替之前的delegate回调.

比传统的UIAlertView好用的地方就是block代替了delegate.

• (id)showAlertWithTitle:(NSString *)title message:(NSString *)message completionBlock:(void (^)(NSUInteger buttonIndex, EMAlertView *alertView))block cancelButtonTitle:(NSString *)cancelButtonTitle otherButtonTitles:(NSString *)otherButtonTitles, ...;