Add support for parsing negative stop-time values in stop_times.txt
Change semantics of negative stop times.  A value of "-1:35:00" is
equivalent to "23:35:00 on the previous day.
Add an AgencyAndId convenience method to MockGtfs.
Refactor CalendarSimplificationLibrary such that it doesn't depend on
CalendarService directly.
Introduce a transform to "fix" negative stop-times in stop_times.txt
(aka trips that start before midnight on a given service date).
Merge branch 'master' of https://github.com/OneBusAway/onebusaway-gtfs-modules.git