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/_pages/year-archive.html

@@ -0,0 +1,17 @@
+---
+layout: archive
+permalink: /year-archive/
+title: "Posts by Year"
+author_profile: true
+---
+
+{% include base_path %}
+{% capture written_year %}'None'{% endcapture %}
+{% for post in site.posts %}
+  {% capture year %}{{ post.date | date: '%Y' }}{% endcapture %}
+  {% if year != written_year %}
+    <h2 id="{{ year | slugify }}" class="archive__subtitle">{{ year }}</h2>
+    {% capture written_year %}{{ year }}{% endcapture %}
+  {% endif %}
+  {% include archive-single.html %}
+{% endfor %}