TlsListenerConfig with buffer, or Read trait

[ratmice]

afaict the TlsListenerConfig currently requires sending it PathBuf's, which eventually opens/reads the keys and certs, it would be nice if there were a way to pass it an &[u8] or more likely something implementing the Read trait, so you can use keys and certs that aren't stored on the filesystem.

                TlsListener::build()
                    .addrs("localhost:4433")
                    .cert(cert_path)
                    .key(key_path),