Also bump fix version

Also suppress UnsafeLoaderWarning in ruamel.yaml.

Use QDesktopWidget to get display size instead of from QApplication
instance, which helps with testing.

Add default values to MainWindow constructor.

Refactor widget and Widget to main_widget and MainWidget.

Improve some error handling by using raise instead of printing then
sys.exit(1).

https://github.com/pytest-dev/pytest-qt/issues/206
https://github.com/pytest-dev/pytest-qt/blob/master/.travis.yml

Add some type hinting.

Also add more details to README and move back tox config to tox.ini due
to flake8 not supporting pyproject.toml yet.
https://gitlab.com/pycqa/flake8/issues/428