Updated the script to :-
 * Fix a bug where stop IDs were being read and used in one part of the
   route segments handling code, and stop names in another part.
   Standardised on names for now pending final decision with Herve.
 * Updated the service day handling, so can now potentially specify
    different service frequency patterns on different service days
    (The latter of which GTFS calls "service periods".)
    For now though, have hard-coded all routes to have the same service
     pattern (controllable by the lists at the top of the script,
     DEFAULT_SERVICE_INFO and default_service_headways.