Create show_route_dates.py

For the main Chicago service providers available at TransitFeeds.
URLs that work for this specific script (since they all use similar schema):
Smaller Metra GTFS: "http://transitfeeds.com/p/metra/169/1409025601/download"
Larger CTA GTFS: "http://transitfeeds.com/p/chicago-transit-authority/165/download"
Smaller Pace GTFS: "http://transitfeeds.com/p/pace/171/1408325192/download"
When calling "python show_route_dates.py 'url'" from command line