Move gh-pages branch files into /docs and add test files

- Jekyll ignore `/docs` and `/test` folders when using from root
- Update Staticman config to point to correct branch and data file location
- Replace `{{ base_path }}` references with `absolute_url` filter
- Update documentation

docs/_includes/toc

@@ -0,0 +1,7 @@
+<aside class="sidebar__right">
+<nav class="toc" markdown="1">
+<header><h4 class="nav__title"><i class="fa fa-{{ include.icon | default: 'file-text' }}"></i> {{ include.title | default: site.data.ui-text[site.locale].toc_label }}</h4></header>
+*  Auto generated table of contents
+{:toc .toc__menu}
+</nav>
+</aside>