Allow empty redirect path

[Emilgardis]

twitch_oauth2/src/tokens/user_token.rs

Lines 297 to 305 in 80f1944

	/// The `url` crate converts empty paths into "/" (such as `https://example.com` into `https://example.com/`),
	/// which means that you'll need to add `https://example.com/` to your redirect URIs (note the "trailing" slash) if you want to use an empty path.
	///
	/// To avoid this, use a path such as `https://example.com/twitch/register` or similar instead, where the `url` crate would not add a trailing `/`.
	pub fn new(
	client_id: impl Into<ClientId>,
	client_secret: impl Into<ClientSecret>,
	redirect_url: url::Url,
	) -> UserTokenBuilder {

this is a todo I want to try to fix