Release v0.4.0

This minor release features a redesign of the alternate screen API.

The alternate_screen module has been renamed to just screen. In the screen module, there is now a ScreenController trait which defines 2 methods: enter_alternate_screen and leave_alternate_screen. It is automatically implemented for any type implementing std::io::Write. This implementation does not automatically disable the alternate screen on Drop.

If the user wants to opt-in to making sure the alternate screen is disabled when the program exits, there is a ScreenControllerGuard struct wrapping any struct implementing ScreenController which adds disable-on-drop behaviour.