Set up CI

[withoutboats]

Not sure if this will be tricky - we need to make sure we have as recent as possible a Linux kernel to be able to actually test io_uring functionality.

[withoutboats]

Looked into setting this up with GitHub Actions.. latest version of Linux available is 5.4 through Ubuntu-20.04. This is not late enough to run our test suite successfully. Not sure how to achieve this since CI services usually run on stable distros with relatively old kernels (at least 1 year old) and io-uring is under active development.