Implement using "CONNECT" for tunneling HTTPS through proxy

See #1

*In some situations, it can be necessary to force the usage of a given crypto methods. You can specify the method along with the URL, e.g. `https+v3://example.com` to use SSLv3, `https+tls://exmple.com` to use TLS. Other options are `+v2` and `+v23`.*