* Add err.sh link for threw undefined

* Update wording
Co-Authored-By: Nijjk <22380829+ijjk@users.noreply.github.com>

* Show a better error when someone throws undefined

* Update error wording
Co-Authored-By: Nijjk <22380829+ijjk@users.noreply.github.com>

* Update error wording in test
Co-Authored-By: Nijjk <22380829+ijjk@users.noreply.github.com>

* Update test and add check for statusCode
before updating error

Fixes: #6497 

Upgrades `standard` to major version 12

* Add initial AMP implementation

* Implement experimental feature flag

* Implement feedback from sbenz

* Add next/amp and `useAmp` hook

* Use /:path*/amp instead

* Add canonical

* Add amphtml tag

* Add ampEnabled for rel=“amphtml”

* Remove extra type

Followup to removing the /_error in the initial markup we can now compile it using on-demand-entries only when it's needed.

This reverts commit 9112f63e.

* Move phases back to next/constants

* Fix typescript error

This brings us one step closer to outputting serverless functions as renderToHTML now renders the passed components, which allows us to bundle the renderToHTML function together with statically imported components in webpack.

As I detailed in [this thread on Spectrum](https://spectrum.chat/?t=3df7b1fb-7331-4ca4-af35-d9a8b1cacb2c), the dev experience would be a lot nicer if the server started listening as soon as possible, before the slow initialization steps. That way, instead of manually polling the dev URL until the server's up (this can take a long time!), I can open it right away and the responses will be delivered when the dev server is done initializing.

This makes a few changes to the dev server:

* Move `HotReloader` creation to `prepare`. Ideally, more things (from the non-dev `Server`) would be moved to a later point as well, because creating `next({ ... })` is quite slow.
* In `run`, wait for a promise to resolve before doing anything. This promise automatically gets resolved whenever `prepare` finishes successfully.

And the `next dev` and `next start` scripts:

* Since we want to log that the server is ready/listening before the intensive build process kicks off, we return the app instance from `startServer` and the scripts call `app.prepare()`.

This should all be backwards compatible, including with all existing custom server recommendations that essentially say `app.prepare().then(listen)`. But now, we could make an even better recommendation: start listening right away, then call `app.prepare()` in the `listen` callback. Users would be free to make that change and get better DX.

Try it and I doubt you'll want to go back to the old way. :)

It's no longer needed inside the `render()` function since we have a separate devServer

As prepare is only needed to boot up the hot reloader + exportPathMap routes in development, it's not longer a requirement in the production server.

- Implements Lerna
- Moves all source code into `packages/next`
- Keeps integration tests in the root directory

Remove `if(this.hotReloader)` as it's always guaranteed to be there.

https://github.com/zeit/next.js/pull/5317#discussion_r221233064

* Initial dev server

* Remove obsolete check

* Move hotReloader to dev-server

* Use parent renderErrorToHTML to remove dep on render.js

* Remove dev option from server itself