* [Rust] Move request logic into standalone file
This reduces the number of variables which are used in the generated
operations, thus fixing #512.
This also fixed a TODO related to URI parsing errors.
Other than that, it is meant to be functionally identical.
* [Rust] Add support for non-file form params
Up until now, they just weren't there at all
* [Rust] Use more rustic terms in example
* Use the right package name for the Rust crate.
* Change getters on models to return Option for non-required fields.
* Cleanup Rust generation and get example compiling again.
* Use underscore names for functions.