Function spawn_sender_task 

pub fn spawn_sender_task(
    stream: TcpStream,
    enc: EncryptedSession,
    frame_kind: FrameKind,
    perm_auth_key: Option<[u8; 256]>,
) -> (SenderHandle, Receiver<FrameEvent>)

Spawn the sender task. Returns a SenderHandle for the client and an mpsc::Receiver<FrameEvent> for receiving update bodies and errors.