Result: document occupancy accessor

Returns the "mode of transport", for instance "zug", "s-bahn", "tram" or

"sonstige".

=item $departure->occupancy

Returns expected occupancy, if available, undef otherwise.

Occupancy values are passed from the backend as-is. Known values are

"MANY_SEATS" (low occupation), "FEW_SEATS" (high occupation), and

"STANDING_ONLY" (very high occupation).

=item $departure->platform

Departure platform number (may not be a number).