* Add method: justify
* Add justify test
* Add another justify test
* Please the linter
* Allow single-item text_list in _rearrange_into_cols()
* Add parameter checks to software_columns
* Test for specific errors
* remove type comment where type is annotated
* move function tests
* remove six from tests
* add none annotations
* add more types
* change mock (so that mypy understands it)