Publish to crates.io

I search crates.io to find crates wrapping datafrog by checking its ["dependents" tab](https://crates.io/crates/datafrog/reverse_dependencies), and didn't see this crate. (I found it via a [Polonius issue](https://github.com/rust-lang/polonius/pull/132).) It might be good for discoverability to pop the crate onto crates.io