Use serde to more easily get query parameters

[BrandonDyer64]

Allows the user to do something like this:

#[derive(Deserialize)]
struct MyQueryParams {
    a: i32,
    b: bool,
    c: String,
}

router.get("/route", |req, _ctx| {
    let query: MyQueryParams = req.query()?;

    // ?a=2&b=true&c=Hello
    assert_eq!(
        query,
        MyQueryParams {
            a: 2,
            b: true,
            c: "Hello".into(),
        }
    );
})

This is the inverse implementation of what reqwest does for building queries using serde.