Crate maintenance

Hi! I'm starting a new [Rust debugger project](https://github.com/headcrab-rs/headcrab/) which heavily depends on `mach` for the macOS target implementation. I would love to help with maintenance of this crate: reviewing pull request, keeping the code up to date with rustc updates, improving documentation, adding missing headers, etc. How can I do this? cc @gnzlbg

Thank you.

No specific file, test, or entry point is named. Start by reviewing the mach crate's current Rust, documentation, and macOS/Mach header maintenance needs, then clarify one concrete task and its acceptance criteria before beginning.

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