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/2012-03-14-layout-excerpt-generated.md

@@ -0,0 +1,17 @@
+---
+title: "Layout: Excerpt (Generated)"
+excerpt_separator: "<!--more-->"
+categories:
+  - Layout
+  - Uncategorized
+tags:
+  - content
+  - excerpt
+  - layout
+---
+
+This is the post content. Archive-index pages should display an auto-generated excerpt of this content.
+
+<!--more-->
+
+Be sure to test the formatting of the auto-generated excerpt, to ensure that it doesn't create any layout problems.