message: Changed misleading mousewheel event documentation.
  Now reflects SDL2 documentation, and reality (as tested on a Windows 10 PC with a generic mouse).
diff: @@ -97,7 +97,8 @@ pub trait EventHandler {
  ) {
  }
  - /// The mousewheel was clicked.
  + /// The mousewheel was scrolled, vertically (y, positive away from and negative toward the user)
  + /// or horizontally (x, positive to the right and negative to the left).
  fn mouse_wheel_event(&mut self, _ctx: &mut Context, _x: i32, _y: i32) {}
  /// A keyboard button was pressed.
  