Python package

[gadomski]

Closes

• Closes #195

Description

Adds a new crate, pystac, which is a Rust-backed Python package named pystac_rs. Currently just a proof-of-concept.

Checklist

Delete any checklist items that do not apply (e.g. if your change is minor, it may not require documentation updates).

• [ ] Unit tests
• [ ] Documentation, including doctests
• [ ] Git history is linear
• [ ] Commit messages are descriptive
• [ ] (optional) Git commit messages follow conventional commits
• [ ] Code is formatted (cargo fmt)
• [ ] cargo test
• [ ] Changes are added to the CHANGELOG