1. Renamed Stretch class to Journey (as per decision in Rostering algorithm document) and updated it to:
  + use Calendar class instead of Date class
  + use an external method I wrote elsewhere for formatting Calendar objects as strings
2. Implemented BusStop, Route and Service classes to support Timetable class
3. Implemented get_journeys() method in Timetable class, this is the first stage of the rostering process.
4. Bug fixed and added a few useful methods to the database wrapper classes.