Amethyst Pong Tutorial

This project follows the Amethyst pong tutorial :

https://book.amethyst.rs/master/pong-tutorial.html

To run the game, run the following command, which defaults to the vulkan graphics backend:

cargo run

Windows and Linux users may explicitly choose "vulkan" with the following command:

cargo run --no-default-features --features "vulkan"

Mac OS X users may explicitly choose "metal" with the following command:

cargo run --no-default-features --features "metal"