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/_pages/404.md

@@ -0,0 +1,16 @@
+---
+title: "Page Not Found"
+excerpt: "Page not found. Your pixels are in another canvas."
+sitemap: false
+permalink: /404.html
+---
+
+Sorry, but the page you were trying to view does not exist --- perhaps you can try searching for it below.
+
+<script type="text/javascript">
+  var GOOG_FIXURL_LANG = 'en';
+  var GOOG_FIXURL_SITE = '{{ site.url }}'
+</script>
+<script type="text/javascript"
+  src="//linkhelp.clients.google.com/tbproxy/lh/wm/fixurl.js">
+</script>