Set up CI with that checks fmt, runs `cargo check` and runs the tests

[marotili]

We should set up a basic CI that runs

• cargo fmt -- --check
• cargo check
• cargo test --all

[marotili]

@erlend-sh My knowledge here is very limited. Imo we should use the same stack as Amethyst. Would that be possible?

[erlend-sh]

Moved to forum since it's at the discussion stage, not ready for implementation.