message: Add graphics::present to State::draw boilerplate
diff: @@ -24,6 +24,7 @@ impl ggez::event::EventHandler for State {
  Ok(())
  }
  fn draw(&mut self, _ctx: &mut Context) -> GameResult {
  + graphics::present(ctx)?;
  Ok(())
  }
  }
  @@ -80,6 +81,7 @@ fn draw(&mut self, ctx: &mut Context) -> GameResult {
  graphics::WHITE,
  )?;
  graphics::draw(ctx, &circle, graphics::DrawParam::default())?;
  + graphics::present(ctx)?
  Ok(())
  }
  ```
  @@ -116,6 +118,7 @@ fn draw(&mut self, ctx: &mut Context) -> GameResult {
  graphics::WHITE,
  )?;
  graphics::draw(ctx, &circle, graphics::DrawParam::default())?;
  + graphics::present(ctx)?;
  Ok(())
  }
  ```
  @@ -157,6 +160,7 @@ fn draw(&mut self, ctx: &mut Context) -> GameResult {
  graphics::WHITE,
  )?;
  graphics::draw(ctx, &rect, graphics::DrawParam::default())?;
  + graphics::present(ctx)?;
  Ok(())
  }
  ```
  @@ -238,6 +242,7 @@ fn draw(&mut self, ctx: &mut Context) -> GameResult {
  // ...and then draw it.
  graphics::draw(ctx, &mesh, graphics::DrawParam::default())?;
  }
  + graphics::present(ctx)?;
  Ok(())
  }
  ```
  