Depends on https://github.com/zeit/next-plugins/pull/228
Failing tests are expected as `@zeit/next-css` has to be updated/released first.
This implements rendering of `.css` chunks. Effectively removing the custom document requirement when adding next-css/sass/less/stylus.
Fixes#4686
Adds tests for @zeit/next-typescript so that we don't regress on this again.
I've fixed an issue in the `next` CLI too which caused lingering processes when the process gets force killed, which is what we do in the test suite, so it kept running if there was no manual quit.
* Add next/config
* Set config on server start / client render
* Add documentation for next/config
* Add next/config support for next export
* Fix test
* Use the correct name
* Set default to empty object on the client side
* Add config tests
* Rename config to runtimeConfig
