tidytransit 1.5.0

• introduce as_tidygtfs and primary key check #198
• tidygtfs inherits list class #202
• Use NA for empty arrival/departure time strings #196
• pass on ... argument in read_gtfs to gtfsio::import_gtfs #199
• Fix for dplyr 1.1.1 #197
• depend on gtfsio >= 1.1.0 #201
• update raptor doc #200

Full Changelog: 1.4.1...1.5.0