Version 2.0.0

This is Pico's second major release! 🎉

For a complete list of all changes compared to Pico 1.0, please refer to Pico's CHANGELOG.md (including the three beta releases v2.0.0-beta.1, v2.0.0-beta.2 and v2.0.0-beta.3).

Please refer to Pico's new upgrade docs to find out what has changed and how to upgrade your Pico 1.0 installation to Pico 2.0.

* [New] Add Bountysource
* [Changed] Improve documentation
* [Changed] Improve release & build process
* [Changed] Add `Pico::setConfig()` example to `index.php.dist`
* [Fixed] Don't load `config/config.yml` multiple times