Release checklist

Make sure cargo outdated -R is clean in the root and in b3sum/.
Bump the version in the root Cargo.toml.
Bump the version in b3sum/Cargo.toml.
- Bump the dependency version too, if new features are used.
Delete b3sum/Cargo.lock and recreate it with cargo build or similar.
Update the -h output in b3sum/README.md if it's changed.
Bump BLAKE3_VERSION_STRING in c/blake3.h.
Bump VERSION in c/CMakeLists.txt.
Make a version bump commit with change notes.
git push and make sure CI is green.
git tag the version bump commit with the new version number.
git push --tags
cargo publish in the root.
cargo publish in b3sum/.