* Fixed a units problem in the speed calculation and reporting
  (Result was in m/s, now properly converted to km/h)
* Added rounding of speeds option in CSV output, and default to 2 dec places.
* Added reporting of seg distance to CSV speeds output file.
Just added closing of an open file at end of script for cleanup purposes.
Added to the speed calculation along route segments function:- the ability to
calculate an average speed over several nearby segments, based on a minimum
distance or time to include.

This is necessary because for many GTFS timetables, stop times are specified
at only the minute granularity :- thus for closely-placed stops, this means
calculated speeds can be very lumpy when done only one segment at a time (or
even infinite speeds calculated due to two consecutive stops having the same
visit time listed).
Added new script to create the stops part of the 'abstract network topology'
format (as an ESRI shapefile) from an existing GTFS.

The idea here is that this topology can be modified or extended, to allow
creating a modified GTFS timetable with SimpleGTFSCreator.
Just cleaning up some variable names and remove pdb statements.