* [Rust] Use serde Value for objects
This hopefully fixes the previous TODO; it at least fixes compilation
errors for the specific swagger model I'm working with.
* [Rust] Update Cargo.toml to specify versions
Letting the version float freely is scary, to say the least.
This gives it a better chance at being future-proof.
When the crate author had a recommended selector I picked that,
otherwise I went semver compatible.
* [Rust] Regenerate the example
