Log Message:
Version 2.6.0:

* Added PEP-495-compatible methods to address ambiguous and imaginary dates in
time zones in a backwards-compatible way. Ambiguous dates and times can now
be safely represented by all dateutil time zones.

* Added new methods for working with ambiguous and imaginary dates to the tz
module. datetime_ambiguous() determines if a datetime is ambiguous for a given
zone and datetime_exists() determines if a datetime exists in a given zone.
This works for all fold-aware datetimes, not just those provided by dateutil.

* Fixed an issue where dst() in Portugal in 1996 was returning the wrong value
in tz.tzfile objects

* Fixed an issue where zoneinfo.ZoneInfoFile errors were not being properly
deep-copied.

* Refactored tzwin and tzrange as a subclass of a common class, tzrangebase, as
there was substantial overlapping functionality. As part of this change,
tzrange and tzstr now expose a transitions() function, which returns the
DST on and off transitions for a given year.

* Deprecated zoneinfo.gettz() due to confusion with tz.gettz(), in favor of
get() method of zoneinfo.ZoneInfoFile objects.

* For non-character, non-stream arguments, parser.parse now raises TypeError
instead of AttributeError.

* Fixed an issue where tzfile objects were not properly handling dst() and
tzname() when attached to datetime.time objects.

* /usr/share/lib/zoneinfo was added to TZPATHS for compatibility with Solaris
systems.

* tzoffset and tzrange objects now accept either a number of seconds or a
datetime.timedelta() object wherever previously only a number of seconds was
allowed.

* datetime.timedelta objects can now be added to relativedelta objects.

* Refactored relativedelta.weekday and rrule.weekday into a common base class
to reduce code duplication.