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/post_pagination.html

@@ -0,0 +1,14 @@
+{% if page.previous or page.next %}
+  <nav class="pagination">
+    {% if page.previous %}
+      <a href="{{ page.previous.url | absolute_url }}" class="pagination--pager" title="{{ page.previous.title | markdownify | strip_html }}">{{ site.data.ui-text[site.locale].pagination_previous | default: "Previous" }}</a>
+    {% else %}
+      <a href="#" class="pagination--pager disabled">{{ site.data.ui-text[site.locale].pagination_previous | default: "Previous" }}</a>
+    {% endif %}
+    {% if page.next %}
+      <a href="{{ page.next.url | absolute_url }}" class="pagination--pager" title="{{ page.next.title | markdownify | strip_html }}">{{ site.data.ui-text[site.locale].pagination_next | default: "Next" }}</a>
+    {% else %}
+      <a href="#" class="pagination--pager disabled">{{ site.data.ui-text[site.locale].pagination_next | default: "Next" }}</a>
+    {% endif %}
+  </nav>
+{% endif %}