Delegate variable is strong

Shouldn't

    static id<AppiraterDelegate> _delegate;

be

    __weak static id<AppiraterDelegate> _delegate;

instead?

Usually, all delegates are weak to avoid retain cycles in delegates of non-singleton objects. This shouldn't be as much of a problem with a Appirater, which only has class methods (similar to a singleton) but still I think it's best practice to declare the delegate as `__weak`.