feature: Navigate to a page then remove previous one from stack

[BoutemineOualid]

Feature Request
I would like to achieve the following behavior:
Once I navigate to a page, I would like to remove the previous page from the stack. Something like

			this
				.HostScreen
				.Router
				.NavigateAndRemovePrevious
				.Execute(targetViewModel)
				.Subscribe()
				.DisposeWith(Subscriptions);

What is the current behavior?

I tried mimicking this behavior by manually removing the previous entry from the Router's NavigationStack but that resulted in an animated back navigation then forward navigation to my target vm.

[glennawatson]

Hi there.

We are revamping the stack navigation in the future so might be worth adding this to our rfc here reactiveui/rfcs#20