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/2009-08-06-edge-case-no-body-content.md

@@ -0,0 +1,9 @@
+---
+title: "Edge Case: No Body Content"
+categories:
+  - Edge Case
+tags:
+  - content
+  - edge case
+  - layout
+---