* leapseconddata.tai is a timezone object. BEWARE, because of reasons,
it compares equal to datetime.datetime.utc!
* tai_offset can take either kind of timestamp
* to_tai, tai_to_utc: convert to/from the TAI timescale.
* is_leap_second: return True if the given second is a leap second.
In the UTC timescale, the ":59" second returns True even though
"only" the second repetition of :59 is a leap second
* Our own error types (squee, such cute little classes)
* check_validity of a timestamp without exceptions
* tai_offset always returns a timedelta now
* add from_standard_source, searches standard linux & freebsd locs, then
goes to the network for ietf
* reformat some test-run messages so they don't trigger my editor's
"error on file and line" regular expression matching
* lightly use logging
