This directory is not public facing, it contains assets used for building bundles.

It makes the repository slightly cleaner and makes things like linting easier.

* Do not run `npm install` in assets twice when running `dist` script.
* Install also PHP dependencies in post-install (re-use the `install-dependencies` target`).
* Use node executable from NPM via environment variable, instead of relying for it to be on PATH (which is not the case since NPM 4, see https://docs.npmjs.com/cli/run-script).
* Print filename of the generated archive in `dist` script.

Also follow semantic versioning so consumers are better informed about breakage.

https://semver.org/

This will allow clients to obtain version of Selfoss and API, as well as the the instance configuration. The configuration options are not part of the public API yet, though.

I put it under /api prefix, as we might move the rest of the API there in the future.

Increases API version to 2.20.0 – new feature

We will try to load fresh configuration from the server each time selfoss is opened and cache it in the localStorage indefinitely.

If configuration cannot be feched (e.g. in offline mode), the value from localStorage will be used.

The use of template strings make this commit unusable in older browsers until we start transpiling with Parcel.
It is not so bad: https://caniuse.com/#feat=template-literals

So that we can make the templates completely static.

Also fix some invalid HTML and meta parity.

These use their own salt so it will make them easier to generate on the client. We still support the old password scheme with separate salt so users did not have to rehash their passwords.

Just like with the `selfoss.config` replacing the `data` attribute lookup, we should use the existing `selfoss.ui._` function. This will make changing the translation method easier in the future.

Setting `<base>` in the HTML files was not actually necessary, since we do not use subdirectories in our front-end routes. When we start using history API, it will not be necessary either, as long as we know the routes. The base URI is therefore only necessary for cookies and RSS feed.

Using asset bundler will allow us to switch to modern JavaScript, build user interface client-side more easily, and develop iteratively thanks to hot module replacement.

We chose Parcel over Webpack for simplicity of set up.

With this, selfoss no longer supports run-time minification of assets. Instead, developer will need to run `npm run build` to bundle all the dependencies and our files and copy them to the `public/` directory. This means the directory is no longer needed to be writeable at run time (useful for read only locations). Alternately, developer can run `npm run dev` command, which will start a program that will watch selfoss files, rebuild them in the background when changed, and then, refresh the opened page. For common users, there are prebuilt packages available, or they can use user.{css,js} for customization, as before.
The routes `GET /` (without AJAX), `GET /password` and `GET /opml` were turned into primitive servers of static HTML files and all the magic is happening client-side. OPML is uploaded completely using XHR and even the password hash is generated client-side.

We started using some EcmaScript 6 features like imports, which Parcel will automatically resolve.

Languages are imported statically as well, to avoid having to copy them using `parcel-plugin-static-files-copy`. Unfortunately, it requires us to declare them explicitly for Parcel to be able to resolve them.

We are using `parcel-plugin-sw-cache`, which uses `workbox` to generate ServiceWorker boilerplate. We do not use the Workbox library, though, as it is not possible to both load it locally (not from CDN) and customize the service worker – we just rely on it to get the list of files into the worker.

Since these are supposed to be editable by user any time and we do not want to require users to install development environment, we will need fetch these files manually and handle cache invalidation ourselves. As a key, we will use their mtimes, which we will pass through the configuration key of `/api/about` endpoint. This is re-fetched whenever selfoss is opened, so we can notice when the files are modified, and we will add them to browser's cache storage. Service worker will ignore those cache keys.