Switch to GitHub actions for CI and Publishing

[bradfier]

Switch us over to GitHub Actions now that Travis is ending its support for Open Source projects.

Also bumps our MSRV to 1.41.1, as tiny-http 0.6.2 depends on a version of url that requires rustc >= 1.36, so we need to increase it to at least that, and the current 'in the wild' versions of Rust look like this:

• Debian OldStable: 1.41.1
• Debian Stable: 1.41.1
• RHEL 8.2.1: Rust 1.42
• RHEL 8.3: Rust 1.45
• CentOS 8 (as of today, it's a rolling release now): Rust 1.45

@tomaka could you please set a Crates.io token in the GitHub actions secrets as CARGO_REGISTRY_TOKEN and remove Travis from the 'required CI steps' settings if it's there? Once that's done, I can merge this.

[tomaka]

Done, but the linting fails

[bradfier]

Done, but the linting fails

Thanks! I'll comment out the format linter for now and do a rustfmt run separately.