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/page__taxonomy.html

@@ -0,0 +1,7 @@
+{% if site.tag_archive.type and page.tags[0] %}
+  {% include tag-list.html %}
+{% endif %}
+
+{% if site.category_archive.type and page.categories[0] %}
+  {% include category-list.html %}
+{% endif %}