support frequencies.txt

[derhuerst]

frequencies.txt represents trips that operate on regular headways (time between trips). This file can be used to represent two different types of service.

Frequency-based service (exact_times=0) in which service does not follow a fixed schedule throughout the day. Instead, operators attempt to strictly maintain predetermined headways for trips.
A compressed representation of schedule-based service (exact_times=1) that has the exact same headway for trips over specified time period(s). In schedule-based service operators try to strictly adhere to a schedule.

https://gtfs.org/reference/static/#frequenciestxt

These files will have to be adapted:

• compute-stopover-times
• compute-connections
• compute-schedules
• compute-sorted-connections