Switch CI to GitHub Actions #93
Description
- Set up GitHub Actions (Use GitHub Actions for CI #91)
- Either define a Windows toolchain or remove Windows from the matrix (Add a Windows toolchain #94, Disable Windows on CI #95)
- Fix the cache directories - apparently the cache directories aren't created and GitHub Actions isn't saving anything
- Figure out why the example targets are building on macOS and locally but not on Ubuntu on CI
- Clean-up Cirrus