Updated the GTFS script so that the route segment processing is now in
 the outermost loop, and so only happens twice per route (once in both
 directions).

This speeds up the script quite a bin in cases of e.g. multiple service
periods ("monfri", "sat", sun" etc) as it means the route-processing
happens considerably less.

Cuts the time for the BZE 80 routes at high frequency schedule generation
time down from ~11 minutes to ~7 minutes.