Version 2.1.0-beta.1

```
* [Changed] Add basic `pico-theme.yml` to use API v3, enable Twig's autoescape
            feature (no changes necessary) and register `Social` meta header
* [Changed] Use Pico's `pages` Twig function to create the main navigation
* [Changed] Improve formatting of definition lists and inline code snippets
* [Changed] Improve JSDoc class docs
```