- Removed `fetchRoute` as it was only used once (internal method, non-breaking)
- Convert files to TypeScript
- Don't extend `ServerRouter` from `Router` as it introduces unneeded overhead, we only have to provide `pathname` `asPath` and `query` for `withRouter`. Also added `events` even though it shouldn't be called on SSR, just making sure we don't break things.
This PR aims at replacing next-server/lib/event-emitter.js by mitt.
Fix https://github.com/zeit/next.js/issues/4908
event-emitter.js is ~400 bytes gzipped vs mitt is 200 bytes