feat: add pong example

[RodrigoDornelles]

I'm a beginner at ginga and lua, this is my first game, I made it as a hello world, a simplified view is interesting for other beginners.

I wanted to make a fluid game.

https://github.com/TeleMidia/ginga/assets/29123479/df5d481e-1e0a-4244-88f4-8d1aa986145d

[rafael2k]

Muito legal mesmo @RodrigoDornelles ! Vou dar uma olhadinha antes de mergear.

[RodrigoDornelles]

@rafael2k I was trying to solve a bug, reported #190, but it never worked out, I thought of a simpler and more effective solution.

I consider that pong is done, and tested on real hardware!

https://raw.githubusercontent.com/RodrigoDornelles/RodrigoDornelles/master/media/ginga-pong.gif

[RodrigoDornelles]

@alanlivio @rafael2k não tenho mais ajustes a considerar, está bom no estado que está! inclusive validei em diversos modelos de televisão!

[rafael2k]

Merged! Thanks!