Add support for Format on Save

[corysimmons]

standard-formatter doesn't work and doesn't seem well-maintained. It also means we have to install multiple plugins.

It'd be nice if you added a settings checkbox for Format on Save.

I understand there is a separation of concerns, but literally no user will hurt from this addition.

[sonicdoe]

I already had this at the back of my mind and I’m all for it. As soon as we implement #129, auto-formatting on save won’t be too big of an issue to implement.

[corysimmons]

Thank you! 🙇