Usage:

1. Add this to your Stage:

	.with_pass(amethyst_imgui::DrawUi::default())

2. Add this to your handle_event:

	amethyst_imgui::handle_imgui_events(data.world, &event);

3. Add this to the beginning of your main update:

	let ui = amethyst_imgui::open_frame(state.world);
	if let Some(ui) = ui {
		ui.show_demo_window(&mut true);
	}

4. Add this to the end of your main update:

	if let Some(ui) = ui { amethyst_imgui::close_frame(ui) }