v2.1 update

- fixed timestamp of changes entry for v2.0
- skipped test using MainWindow for computers not having a display
- removed self-made test suite and replaced by Test::More
- bumped Tk requirement to Tk 804.030 because I can't / don't want to
test for an older Tk
- removed bugs section from POD because bumping Tk version requirement
makes bug notice obsolete
- removed METHDOS section from POD as there are no met hods to document
- removed duplicate BUGS section
- added example to POD
fixed things I missed for v2.1

- POD error
- MANIFEST does not contain the old test suite anymore