Improved comments. No functional changes.
Determined how to log SQL parameters without logging huge amount of
other cruft.
Fixed problem with timezone. Had to set it so that data is parsed
properly.
Changed batch size for loading arrival/departure data to 500,000 instead
of 50,000 because found that when doing subsequent fetches it takes
almost as long as loading all of the data in the first place. Fetching
by batch size really slows things down. Only reason to use it is to
prevent too much memory from being used at once.

Also, change key used for maps to be a MapKey instead of a string
concatenation of trip & stop IDs. This is much more foolproof plus one
can easily understand the keys when debugging.