db-iris, Result.pm: Document additional_stops and canceled_stops

=over

=item a / additional

If a train's route deviates from its schedule: Print a list of additional

(unscheduled) stops it will stop at.

=item c / canceled

If a train's route deviates from its schedule: Print a list of canceled

stops (scheduled stops which will not be served).

=item d / delay

If a train is delayed, show the most recent reason for this delay.

=over

=item $result->additional_stops

Returns served stops which are not part of the schedule. I.e., this is the

set of actual stops (B<route_post>) minus the set of scheduled stops

(B<sched_route_post>).

=item $result->arrival

DateTime(3pm) object for the arrival date and time. undef if the

train starts here. Contains realtime data if available.

=item $result->canceled_stops

Returns stops which are scheduled, but will not be served by this train.

I.e., this is the set of scheduled stops (B<sched_route_post>) minus the set of

actual stops (B<route_post>).

=item $result->classes

List of characters indicating the class(es) of this train, may be empty. This