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/2010-03-07-post-link.md

@@ -0,0 +1,15 @@
+---
+title: "Post: Link"
+categories:
+  - Post Formats
+tags:
+  - link
+  - Post Formats
+link: https://github.com
+---
+
+This theme supports **link posts**, made famous by John Gruber. To use, just add `link: http://url-you-want-linked` to the post's YAML front matter and you're done.
+
+> And this is how a quote looks.
+
+Some [link](#) can also be shown.