新增两种导航方式

常见的导航方式

1. 向前，就一种，以前叫push，现在叫show

- (void)pushViewController:(UIViewController *)viewController animated:(BOOL)animated; // Uses a horizontal slide transition. Has no effect if the view controller is already in the stack.

- (void)showViewController:(UIViewController *)vc sender:(nullable id)sender NS_AVAILABLE_IOS(8_0); // Interpreted as pushViewController:animated:

2. 弹出对话框，是UIViewController的pre方法。

/*
  The next two methods are replacements for presentModalViewController:animated and
  dismissModalViewControllerAnimated: The completion handler, if provided, will be invoked after the presented
  controllers viewDidAppear: callback is invoked.
*/
- (void)presentViewController:(UIViewController *)viewControllerToPresent animated: (BOOL)flag completion:(void (^ __nullable)(void))completion NS_AVAILABLE_IOS(5_0);
// The completion handler, if provided, will be invoked after the dismissed controller's viewDidDisappear: callback is invoked.
- (void)dismissViewControllerAnimated: (BOOL)flag completion: (void (^ __nullable)(void))completion NS_AVAILABLE_IOS(5_0);