Version 2.0.0-beta.1

First beta release of Pico's official default theme for Pico's second major release. This is a pre-release!

Note: Pico's default theme was completely rewritten from scratch for Pico 2.0 and moved to this separate repository. This changelog only provides basic information about the most important changes compared to Pico 1.0. It therefore doesn't include the changes made before this release. The rewrite breaks backwards compatibility (BC).

* [New] Rewrite Pico's default theme from scratch with a much cleaner, more
        modern, but still "stupidly simple" structure; the new theme officially
        supports Internet Explorer 9+ as well as all versions of the major
        desktop and mobile browsers, as long as they are still officially
        supported by their respective vendor
* [New] Pico's default theme is now a fully responsive theme, adapting the
        layout to the viewing environment (desktops vs. tablets vs. smartphones
        vs. ...)
* [New] Add a collapsible page menu for small screens (menu slides up/down)
* [New] Add basic form themeing
* [New] Support a "widescreen" mode, demonstrating how themes can adjust their
        behavior using config parameters (i.e. Pico's `config/config.yml`)
* [Changed] Show top-level pages in the website's navigation only (i.e. show
            `page.md` and `sub/index.md`, but not `sub/page.md`)
* [Changed] Hide pages starting with a `_` in the website's navigation
* [Changed] Move Pico's social icons from `index.md` to `_meta.md`,
            demonstrating how themes can use YAML-only meta pages to support
            dynamic content