support url with authority

[yangby-cryptape]

For #715.

With this PR, the output of the example in #715 will be:

RequestBuilder {
    client: Client,
    request: Ok(
        Request {
            method: POST,
            url: "http://localhost:12345/",
            headers: {
                "authorization": "Basic dXNlcm5hbWU6cGFzc3dvcmQ=",
                "content-type": "application/json",
            },
        },
    ),
}

I checked the logs of nginx, this request was same as the request which sent by curl/7.65.0 with same url and same content.

• If the modification in this PR was acceptable, I can pull another PR to the master branch.

[t-botz]

Triple cloning here. Seems unecessary.
I doubt basic_auth needs an owned object, I am pretty sure you can implement that with absolutely no cloning, just using reference.

[seanmonstar]

I've made some modifications and opened #735, thanks for starting this!