feat: add prettier

[henryiii]

Should be implemented in Cookie first.

[eduardo-rodrigues]

How does this interfere, if at all, with for example Black? This point may be worth a sentence.

[henryiii]

Pretty sure Python is not one of the languages it supports. But that's partially why it has a mention of using types_or to ensure it's not trying to change files you'd rather not be auto formatted. I should include json in the list. I'm pretty sure we don't already recommend an auto formatter for any of the supported file types.

[henryiii]

Updates: I've run prettier on the website itself, and worked out a few things:

• Prettier can format YAML inside codeblocks in markdown! That's great, so I added blacken-docs which does the same thing for Python (Black) inside markdown.
  • This actually found a bug, we had invalid syntax in one example!
• I'm having prettier reflow everything to ~80 chars. We could also have it reflow to no line wrap, I care more about consistency than which setting.
• Pretty mostly is okay with Jekyll, but it does break {: .no_toc} or similar right after a heading by adding a blank line. I've avoided this most places by adding the title directly to the page - you can override the title with custom_title: <>. If you add custom_title but leave it blank, there will be no title at the top.
• I've replaced the ugly capture workarounds with the correct markdown="1" for expandable. Later I'll style the expandable to look more like the current TOC styling.
• There was some slightly broken or non standard YAML that I've cleaned up with prettier's help.

When viewing the diff, be sure to turn off whitespace in Github's viewer, it helps a little bit!