message: Add MsgHeaders type
diff: @@ -179,9 +179,10 @@ pub fn send_handshake(hs: &Handshake) -> Vec<u8> { cbor!(hs).unwrap() }
  type Message = (u8, Vec<u8>);
  pub enum MsgType {
  - MsgSubscribe = 0xe,
  MsgGetHeaders = 0x4,
  + MsgHeaders = 0x5,
  MsgGetBlocks = 0x6,
  + MsgSubscribe = 0xd,
  }
  pub fn send_msg_subscribe(keep_alive: bool) -> Message {
  