Added handshake in data sent during multiplex negotiation

[0xMimir]

Fixes #543, added Token::Handshake in data sent when negotiating multiplexing protocol.

If handshake is not sent with multiplexing protocol during negoation with OCaml node, OCaml node throws error when trying to dial rust node in go-multistream@v0.3.3/client.go:

func readMultistreamHeader(r io.Reader) error {
	tok, err := ReadNextToken(r)
	if err != nil {
		return err
	}

	if tok != ProtocolID {
		return errors.New("received mismatch in protocol id")
	}
	return nil
}

With error: received mismatch in protocol id