This new version of kdl-rs is a complete rewrite that introduces
a formatting-aware-and-preserving parser, much like toml_edit et al.
BREAKING CHANGE: Completely new API and bumped MSRV to 1.56.0.
* Add From impls for KdlNodeValue
Most clients probably don't need to create these directly, but we may as
well make it easy for them.
* Add TryFrom impls to convert from KdlNodeValue to underlying types
This includes converting from borrowed values, which will produce `&str`
instead of `String`.