copy some examples from the manual
Bug fix: $dtm - $interval would return another interval

It was supposed to return a new DTM, but the logic was wrong.
correct examples in documentation
propagate time zone to new object when adding or subtracting
allow calls to ->set_time_zone

DateTime uses it inside of ->from_epoch if a time zone is supplied on cretion, and
DST example test
number of days in month test
dunno what POD2XHTML.pm is but I'm not gonna commit it
allow set_locate and set_formatter; those should be harmless
doc tweaks
move MyDaysInterval into t/lib
fix bugs in dist.ini

It was picking up files that were not part of the distribution.  Using
Git::GatherDir instead of GatherDir tells it only files that are part
of the Git repo should be included in the distribution.
make sure that arithmetic retains the time zone of the original object
tweak docs
warn about mutation via set_time_zone