Add CI

[LiHRaM]

Related to #1, #2

I've created a CI pipeline that checks compilation on all the platforms, and rustfmt as well. Currently it only fails the check if rustfmt fails, because both macOS and Windows are failing anyway.

But it gives us a good idea of where we are platform wise, and it does let you know if the Linux build fails.

Optional Todos:

• [ ] Instead of failing the action if rustfmt checks do not pass, we could have the action automatically fix the formatting errors
• [ ] Add more than just stable rust to the feature matrix, could e.g. include nightly and older versions as a lower bound.
• [ ] Separate macOS/Windows jobs from linux job, failing the check if the linux fails but keeping macOS/Windows optional

Feel free to add any thoughts / improvements as well!

Edit: Example at https://github.com/LiHRaM/buzz/actions/runs/158353787

[jonhoo]

This is excellent, thank you! I'd like to have it also run clippy and build on beta if possible.

[jonhoo]

Thanks!

[LiHRaM]

Ahh... I'm afraid I forgot to add an installing dependencies step. I'll submit a followup pr :smile: