GitHub Actions workflows

Would you be interested in having GA workflows being added to the repository? I could provide you these workflows:
- CI workflow triggered on PRs:
- Does formatting checking
- Runs clippy
- Runs tests
- CD workflow triggered when pushing a git tag:
- Pushes a new version to crates.io

Additionally, the following could be done:
- CI workflow for scheduled spinner updates:
- Runs a cron job to update the spinners automatically. If updates do take place, a new patch version is published.

An alternative to the last workflow would be to turn the `update_spinners` script into a build script. That way, the files are always up-to-date. Compilation would be longer though (maybe 2sec-5sec, depending on the internet connection).