Releasing

Releasing is done with goreleaser. Install it, and check out its docs.
Set a GITHUB_TOKEN environment variable. See goreleaser's docs for more information.
Update CHANGELOG.md:
- Mention recent changes.
- Set a version if there is not one.
- Set a release date.
- Commit.
Tag the release: git tag -a v1.2.3 -m 'Tag v1.2.3'.
Push the tag: git push origin v1.2.3.
Run goreleaser.