Update license format

Update README for 0.4.1

Up rev to 0.4.1

Add timestamp, formatting, emoji and more!

Fix blank display_name issue

Fix "no valid link found" loop

Explain how to apply non-App Store slack support

Explain Python version requirement.

Up rev to 0.4.0. Switch to PyPI's new pyproject.toml format.

Translate user IDs into display names.

Add command line args: -h, -p, -u and -d.

Fix setup.cfg so refactoring of main into slackclipper_runner works.

Refactor main into own module.

Finish first pass readme. Add installation, shortcomings sections, and screenshots.

Tidy up first release. Improve user comms, fix README image, remove dead code, etc.