Extracted the pairs iterator funcs from lineargeom.py into their own file,
misc_utils.py
Added ability to gtfs_ops.py to query, extract and write speed between stop pairs
(segments), in specified time periods of interest.

Note:- currently only does a 'as crow flies' speed, doesn't yet have facility
to look up and calculate/store via actual geometry.
Slightly generalised the route name to route number conversion process to
allow multi-letter prefixes to routes.
In func create_stops_shp_file() :- added code to create needed directory to
put file in, if it doesn't exist already.
in get_route_names_sorted():
 * Changed the sorting so that longer route name strings (I.E. not in the form
    "R04") can be handled ok still

in order_route_segments():
 * Fixed a bug so that routes only containing one segment are still
   ordered ok and a proper route_dirs tuple string is returned.

(Actually did this work about 1 month ago, motivated by needs of the I.P.
project).