Follow-up on the "default fields" feature

[dmerejkowsky]

• [x] Fix mypy error
• [x] Rename 'match' variable (it became a keyword in Python 3.10)
• [x] Update documentation and changelog

[dmerejkowsky]

@minrk : I had a few ideas to improve your patch in #122 - feel free to leave your comments here :)

[dmerejkowsky]

I've also added a task list about what needs to be done before we release a public tbump version containing this feature - feel free to help

[minrk]

Thanks! I took a stab at docs in #127