Improve documentation (#1058)

* Remove @ingroup from class member definitions
* Add the documentation for every public classes.

include/ftxui/component/screen_interactive.hpp

@@ -27,6 +27,10 @@ struct Event;
 using Component = std::shared_ptr<ComponentBase>;
 class ScreenInteractivePrivate;
 
+/// @brief ScreenInteractive is a `Screen` that can handle events, run a main
+/// loop, and manage components.
+///
+/// @ingroup component
 class ScreenInteractive : public Screen {
  public:
   // Constructors: