Added code to route_segs.py full-stop segment topology generation algorithm to
deal with one-segment branch cases.
Cleaned up the code re creating ordered stop list for routes as part of GTFS,
as it wasn't working for one-segment routes.
A small fix to dist-based speed algorithm to use a max distance of 50km from
CBD, else get strange values for some of the outer routes.
Implemented new functions into subset_trips_by_route.py to be able to pass a
shapefile of polygons to use for subsetting routes of interest to only those
within a particular region.