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/2010-10-25-post-future-date.md

@@ -0,0 +1,8 @@
+---
+title: "Post: Future Date"
+date: 9999-12-31
+categories:
+  - Post
+---
+
+This post lives in the future and is dated {{ page.date | date: "%c" }}. When building Jekyll with the `--future` flag it should appear.