Convert an incomikng handshake message into a struct.

Request
MUST include:  * channel
               * version
               * supportedConnectionTypes
MAY include:   * minimumVersion
               * ext
               * id

This struct contains the following keys:

• :channel always "/meta/disconnect".
• :version the Bayeux version the client requires.
• :supported_connection_types the connection types (transports) that the client is capable of negotiating.
• :minimum_version the minimum Bayeux version the client requires. Optional.
• :ext an arbitrary map of data the client sent for use in extensions (usually authentication information, etc). Optional.
• :id a message ID generated by the client. Optional.