* Write BUILD_ID when building.
It's a random id (uuid.v4())
* Add buildId to the core JS files.
* Add immutable cache-control header.
Only if the buildId is matched.
* Set '-' as the dev buildId always.
* Add buildId handling for JSON pages.
* Server JSON pages directly from the filesystem.
* Make Json pages even if there's an error.
* Implement much better page serving.
* Use JsonPagesPlugin in the production mode as well.
* Add gzip support for JSON pages.
* Use glob-promise instead of recursive-readdir
* Handle renderStatic 404 properly.
* Simply the gzip code.
* Cache already read JSON pages.
* Change JSON pages extension to .json.
* Fix HMR related issue.
* Fix hot-reload for .json solely on server.
* Properly clear cache on hot-reloader.
* Convert .js pages into .json page right inside the plugin.
* Fix gzipping .json pages.
* Remove unwanted json pages cleanup.
* Get rid of deprecated fs.exists for fs.access
* Immplement the initial singleton Router.
* Use the new SingletonRouter for HMR error handling.
* Use SingletonRouter inside the Link.
* Create an example app using the Router.
* Make the url parameter optional in Router.push and Router.replace
* Add a section about next/router in the README.
* Remove the use of CDN and bundle everything inside the app.
We still pre-build the prefetcher because it needs
different webpack config which only targets browsers
supports Service Workers.
* Remove cdn config item.
We no longer using it.
* Stop adding script tags when staticMarkup=true
* Remove babel-plugin-transform-remove-strict-mode NPM module.
* add detach-plugin
* detach-plugin: remove unused property
* watch-pages-plugin: replace _error.js when user defined one was added/removed
* dynamic-entry-plugin: delete cache
* fix HMR settings for _error.js
* render: pass error only on dev
* hot-reload: enable to hot-reload error page
* server: check if /_error has compilation errors
* webapck-dev-client: fix reloading /_error
