Replace eslint with xo

[koddsson]

I was doing some exploring and found xo and it looks pretty neat to me. The biggest drawback seems to be that you need to add a xo plugin to your $EDITOR but if that's a big drawback I think we could just extend eslint-config-xo.

I disabled most of the rules but left those that didn't need a lot of work and made sense to me and fixed the issues that xo was reporting.

[benediktvaldez]

LGTM

[benediktvaldez]

Large changeset and doesn't really matter IMHO. XO is great for exactly that reason.

My vote is to fix the conflicts and merge asap

[koddsson]

@benediktvaldez What do you think about people needing to config a different flow for their editor to use xo over eslint?

[benediktvaldez]

The simplest way to solve that would be to create a .eslintrc file in the root with

{
	"extends": "xo"
}

This should work in most editors that support eslint

[koddsson]

Ah lol, of course 😄

[koddsson]

I say we go for this and then we can change to the xo-config if we want to

[koddsson]

Nothing changed in the tests here which makes me believe that the tests might be flaky after #403 😭