Add array deserialize support for duplicate keys (without square brackets)

[vegardgs-ksat]

This PR expands support to handle duplicate keys without square brackets to be parsed as an unordered sequence.

Given the following query params: id=abc&id=def

#[derive(Debug, Deserialize)]
struct Query {
    id: Vec<String>,
}

let query = "id=abc&id=def";
let result: Result<Query, _> = qs::from_str(query);
assert!(result.is_ok());
assert_eq!(result.unwrap(), Query { id: vec!["abc", "def"] });

This PR closes #35.

Given the discussion and prior position taken to not accept this functionality, I am prepared that this may not be accepted. I would like input from the community for alternative crates that may be a better fit. In general, I am looking a complete parsing solution for typical use-cases encountered from OpenAPI specifications for my server-side query parameter handling.

[k01e-01]

this solved my problem, +1

perhaps this should be handled as its own separate config option?

pub struct Config {
    max_depth: usize,
    strict: bool,
    array_nonindex: bool,
};

impl Config {
    pub fn new(max_depth: usize, strict: bool, array_nonindex: bool) -> Self {
        Self { max_depth, strict, array_nonindex }
    }
}