Add test input including new gtfs fields

[vsp-gleich]

Since this library was built gtfs has moved on and added more fields and generally became more complex. Especially the stops can now be very detailed with multiple entries representing various parts of a station (plattform, entrance, boarding area, etc.). The test gtfs feed in this repo here lacks these new fields. However, the gtfs input for Germany uses especially the more detailed stop representation.
https://gtfs.org/getting-started/example-feed/ gives some examples, but they either don't add up to a working gtfs feed (separate files shown as text on website) or do not include recent fields such as location_type and parent_station (sample feed zip linked on top of the website).