+/// Application controller class.
+/// Operates on a state stack that can be modified via ChangeState, PushState,
+/// and PopState.
+/// All state changes are delayed until the looping mechanism gets control again
+/// (i.e. after a top level state function returns, not during).
+/// SDL key events are preprocessed, see app::Input.
+/// The quit event (typically window closed or signal received) is caught and
+/// results in immediate (that is, after the next input loop) termination.
+/// Popped states will be deleted via the plain delete operator on an app::State
+/// pointer.
+/// Timers created by GlobalTimers() operate on actual application time and are
+/// not paused when the current state is paused (as are the timers started by
+/// the app::State members).