Convert an incoming Pixie.Message.Handshake into a response.

Success Response                             Failed Response
MUST include:  * channel                     MUST include:  * channel
               * version                                    * successful
               * supportedConnectionTypes                   * error
               * clientId                    MAY include:   * supportedConnectionTypes
               * successful                                 * advice
MAY include:   * minimumVersion                             * version
               * advice                                     * minimumVersion
               * ext                                        * ext
               * id                                         * id
               * authSuccessful

The struct contains the following keys:

• :channel always "/meta/handshake".
• :version the Bayeux protocol version supported by the server.
• :supported_connection_types the union of transports between the client’s supported connection types and the server’s enabled types.
• :client_id the client ID generated by the server during handshake.
• :error an error message to send to the client explaining why the request cannot proceed. Optional.
• :minimum_version the minimum Bayeux protocol version supported by the server.
• :advice advice from the server about how to handle timeouts, polling intervals, etc. See the Bayeux protocol for more information.
• :ext an arbitrary map of data the server sends for use in extensions (usually authentication information, etc). Optional.
• :id a message ID generated by the client. Optional.
• :auth_successful either true or false. Optional.