Add HTTP Basic Auth support

[agrenott]

Allowing qbittorrent API to be exposed behind standard HTTP basic authentication.

[George-Miao]

I'm thinking of a more generic way of exposing request details to user. What about a Request object that implements IntoFuture? And user can use it like:

qb.call_some_api()
  .map_request(|r| r.do_something())
  .await

What do you think about it?