Targets macOS 10.7 by default.
To enable features added in macOS 10.8, set Cargo feature mac_os_10_8_features. To have both 10.8 features and 10.7 compatibility, also set mac_os_10_7_support. Setting both requires weak linkage, which is a nightly-only feature as of Rust 1.19.
For more experimental but more complete, generated bindings take a look at https://github.com/michaelwu/RustKit.
If you wish to start contributing or even make a one-off change, simply submit a pull request with the code or documentation change and we'll go from there.