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

docs/_config.dev.yml

@@ -0,0 +1,13 @@
+# Develop override settings
+
+url: http://localhost:4000
+
+analytics:
+  provider: false
+
+comments:
+  disqus:
+    shortname            : "mmistakes-dev"
+
+sass:
+  style: expanded