Added new files to allow calculating and assigning motorway status of route
segments. This is important for bus routes, so we can modify the speed and
stop density depending on whether they're on motorways or not.
Modified the assign_speeds script to add functions to use the "on_motorway"
speed when appropriate. Made these the default functions used.
Just removing some debugging commits.
Parameterised the input properly of create_network_topology_and_stops.py, so
it now takes key parameters as cmd-line arguments rather than hard-coding.

(Haven't yet dealt with the transfer networks properly).
Separated out the former create_network_topology_and_stops.py into separate
scripts for creating auto-stops, and segments:
 - create_network_topology_auto_stops.py
 - create_network_topology_segments.py