Document how the formatter works

[munificent]

It's probably not worth writing down every corner of the formatting rules, but it might be good to at least sketch out the main interesting ones like:

• How an inner split forces outer rules to split.
• The logic around breaking call chains.
• How functions and collections are handled in argument lists.

[kegluneq]

@munificent, fixed by blog post?

[munificent]

Mostly. The other half is documenting the actual formatting rules that the solver... solves. Hopefully that won't be as big as the blog post. :)

[munificent]

Much of this is covered by https://journal.stuffwithstuff.com/2015/09/08/the-hardest-program-ive-ever-written/. I don't think we're going to have separate docs that cover all of the specific formatting rules. They are pretty complex and subtle, and docs would likely be either too simplified and wrong, or too complex for any human to want to read. Also, keeping them in sync with the implementation would be a continuing chore.