Rocket extension to permit enums in application/x-www-form-urlencoded forms

This crate is a workaround for https://github.com/SergioBenitez/Rocket/issues/1937.

It is derived from the included serde_json implementation in rocket.

```rust

[derive(Debug, Deserialize)]

[serde(tag = "type")]

enum Body { #[serde(rename = "variantone")] VariantOne(VariantOne), #[serde(rename = "varianttwo")] VariantTwo(VariantTwo), }

[derive(Debug, Deserialize)]

struct VariantOne { content_one: String }

[derive(Debug, Deserialize)]

struct VariantTwo { content_two: String }

[post("/form", format = "form", data = "")]

fn body(data: UrlEncoded) -> String { /.../ } ```

status

Works but not unit tested, nor have local testing affordances for users been added yet.

Supports rust stable and nightly, matching Rocket.

Code of conduct

Please note that this project is released with a Contributor Code of Conduct. By participating in this project you agree to abide by its terms.

Contributing

PR's on Github as normal please. Cargo test and rustfmt code before submitting.