feat: "Learn gfx-hal" chapters 1, 2 & 3

This implements the first three chapters of the "Learn gfx-hal" tutorial[0].

Some take-aways:

- `gfx-hal` is low-level, requiring lots of boilerplate code. It will be
interesting to see the difference once we start migrating the code to
the `Rendy`[1] crate.

- Lots of unsafe code required.

- The `winit`[2] crate is reasonably heavy, providing platform support that
  isn't relevant to the game (at least not yet).

- Both crates are still young, lots of moving targets.

[0]: https://lokathor.github.io/learn-gfx-hal
[1]: https://github.com/rustgd/rendy
[2]: https://github.com/rust-windowing/winit

Author: JeanMertz

.gitignore

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+/target