Read in a GTFS zip file
Details
The core tables are read with explicit column types (ids as character, coordinates as numeric, etc.); any column type not listed is left to fread's detection. Times of day (stop_times arrival/departure, frequencies start/end) are returned as lubridate Periods so values past 24:00:00 are preserved. Tables without an explicit specification are read with automatic types except that `*_id` columns are always character.