See https://github.com/Traewelling/line-colors/blob/main/line-colors.csv

Closes #9

See #11

Thanks to Cassidy Dingenskirchen for a detailed bug report and fix/improvement
suggestions.

Closes #11

The Stop constructor is called lazily and must have access to a hafas
reference for its add_message function and strptime_obj key. If the hafas
object goes out of scope before Journey->route is called, those may have
been garbage-collected already.

Apart from that, the weaken call was useless, since a Stop object does not
store the hafas reference provided in its constructor. So, as soon as
Journey->route is called, the hafas references in @{$journey->{route}} go out
of scope anyways.