Support serializing byte arrays about serde_urlencoded

[nox]

As @SimonSapin says in the issue you linked:

In the WHATWG specification and in the rust-url implementation of application/x-www-form-urlencoded, the keys and values are both Unicode.

This crate also follows the WHATWG spec, so this is out of scope.

[Hexilee]

@nox Could you please take it into consideration again? As almost all bowsers and other HTTP clients support arbitrary bytes encoding, and there are so many HTTP servers receiving urlencoded-form with non-UTF8 string.
In many cases, if the html is sent in non-UTF8 encoding, and form has default value (non-UTF8), then the bowser have to encode it, and, scraper written in Rust also have to do.
If a PR is welcome, I can create one.

[Hexilee]

I really need it, If you persist in your claim, then I have to create a fork.

[nox]

I really need it, If you persist in your claim, then I have to create a fork.

I don't appreciate your tone but you are free to fork it, not like the method you want cannot live outside of serde_urlencoded anyway.