Allow presenting change ids in readable mixed case

[ilyagr]

The idea is that you could put change_id.readable() in you commit template.

The concept of "readable case" focuses on the k-z part of the alphabet that's used for change ids. The
normal hexadecimal alphabet 0-9a-f doesn't have many confusable letters, except
perhaps b and d.

Here is what it looks like for me at the moment (my ids are also shorter than normal, 6 chars instead of 8):

Backstory and design

This is the third attempt at making change ids readable at a glance. Previously,
I was suggesting printing them in uppercase (which I use in my personal config,
but several people disliked the idea since they perceive UPPERCASE as yelling)
or printing half the alphabet in uppercase.

Since then, I found that uppercase doesn't solve all of my issues either, as
it's quite easy to confuse OQ or UV when reading quickly.

So, I now have a variation of the second idea where I carefully pick which
letters to capitalize. See comments and test in the commit for examples.

Checklist

If applicable:

• I have updated CHANGELOG.md
• I have updated the documentation (README.md, docs/, demos/)
• I have updated the config schema (cli/src/config-schema.json)
• I have added tests to cover my changes

[ilyagr]

I think I'll close this for now. I've tried using lowercase ids again (as is the default), and the difference between "readable case" and lowercase doesn't seem compelling enough to be worth the time it will take people to get used to mixed case and understand it.

For reference, I did come up with some artificial examples on Discord where readable case is much better than lowercase. However, I now think they do not show up often enough in practice to be worth moving to "readable case". If my opinion changes, I might reopen this.