------------------
- Updated package infrastructure to follow guidelines described in APE 17, namely
removing astropy-helpers and using tox for setting up testing environments. [448]
- Fix compatibility with astropy 4.x and 5.0. [448,471]
- Fixed default color for ``show_lines`` (was previously transparent, now black). [441]
- Fixed ``set_tick_direction`` to not error due to incorrect reference to ``ax``. [450]
- Fixed compatibility with Matplotlib 3.4. [466]