Version 1.0.3

* [Changed] Improve documentation
* [Changed] Heavily extend nginx configuration docs
* [Changed] Add CSS rules for definition lists to default theme
* [Changed] Always use `on404Content...` execution path when serving a `404.md`
* [Changed] Deny access to `.git` directory, `CHANGELOG.md`, `composer.json`
            and `composer.lock` (`.htaccess` file)
* [Changed] Use Pico's `404.md` to deny access to `.git`, `config`, `content`,
*           `content-sample`, `lib` and `vendor` dirs (`.htaccess` file)
* [Fixed] #342: Fix responsiveness in default theme
* [Fixed] #344: Improve HTTPS detection with proxies
* [Fixed] #346: Force HTTPS to load Google Fonts in default theme