Tool to edit vim config

[coolaj86]

We need machine-friendly ways of editing certain aspects of the config - which will likely require splitting it out into more files and whatnot.

See webinstall/webi-installers#641 (comment).

For example:

vimtool get ale.fixers
vimtool add ale.fixers.markdown prettier

I hesitate to say "we should just do it as JSON and generate the config each time" because that's well outside the convention (whereas having a few extra files is odd, but not crazy), but... 🤷‍♂️