Throw specific exception when service is unavailable.
Rename function.
Add new example with transfer trains.
Refactor provider.
Know if timetable has transfer station.
Define transfer station in Timetable.
Check for transfer type.
Throw descriptive exception.
Check exception message.
Parser must define transfer station.
Refactor parser.
Improve example with transfer station.
Refactor parser: simplify naming.
Improve docs.