Message: document ->code and ->type

Detailed message content. Does not contain newlines.

=item $message->code

Two-digit message code, seems to be only used with messages of type "A".

Details unknown.

=item $message->type

A single character indicating the message type.

The following types are known:

=over

=item A

Generic information about a specific trip such as "WiFi available", "air

conditioning", "DB tickets are not valid here", or "from here on as [line]

towards [destination]".

=item C

"Current information available", possibly more.

=item D

Large-scale disruption, e.g. medical emergency on line.

=item G

Platform change, possibly more.

=item H

Misc stuff such as "Journey contains trains with mandatory reservation" or

"ICE Sprinter".

=item L

Replacement journey

=item M

Free-text infos about construction sites, broken elevators, large events and

similar occasions.

=item P

Journey has been cancelled, possibly more.

=back

=item $message->ref_count

Counter indicating how often this message is used by the requested