test, provide regression files for bug/21

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
fix, don't fix date differences when the day difference is 0

This closes bug/21 (https://github.com/hroptatyr/dateutils/issues/21).

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
Merge branch 'bug/21'

* bug/21:
  fix, don't fix date differences when the day difference is 0
  test, provide regression files for bug/21