Add Github Actions to build sample projects on multiple platforms

[EliteMasterEric]

#70 already exists to create a full test suite, but we can also create an action which simply builds all the existing samples.

This provides a bare minimum of compatibility checking to ensure no compiler errors exist. It wouldn't provide any functionality testing, but it's a start.

[larsiusprime]

ooooh I need to learn how to use this stuff.

[EliteMasterEric]

I'll get it set up for this repo and then I'll point out the relevant files.

This is REALLY nice because it'll run any actions you define on not just all the commits in your repo, but also (if you enable it) pull requests as well.

This puts a big red X on any PR that fails one of your tests, which is HUGE it's so convenient.

[larsiusprime]

I've seen some other repos do this but never taken the time to figure it out myself! Definitely see how it can massively improve productivity. I dickered around with third party CI a few years ago and it was kind of a massive pain; I take it Github has just moved this all on-platform now?