WIP: tzf's Rust port. 
- Documents: https://docs.rs/tzf-rs
- Original Go repo: https://github.com/ringsaturn/tzf
- Binary timezone data: https://github.com/ringsaturn/tzf-rel
- Geometry: use https://github.com/ringsaturn/geometry-rs which is https://github.com/tidwall/geometry's Rust port.