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

test/_posts/2010-08-06-post-image-linked-caption.md

@@ -0,0 +1,21 @@
+---
+title: "Post: Image (Linked with Caption)"
+categories:
+  - Post Formats
+tags:
+  - image
+  - Post Formats
+---
+
+{% capture fig_img %}
+[![Foo](https://farm5.staticflickr.com/4134/4940462712_7c28420b27_b.jpg)](https://flic.kr/p/8wzarA)
+{% endcapture %}
+
+{% capture fig_caption %}
+Stairs? Were we're going we don't need no stairs.
+{% endcapture %}
+
+<figure>
+  {{ fig_img | markdownify | remove: "<p>" | remove: "</p>" }}
+  <figcaption>{{ fig_caption | markdownify | remove: "<p>" | remove: "</p>" }}</figcaption>
+</figure>