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/_sass/_print.scss

@@ -0,0 +1,18 @@
+/* ==========================================================================
+   PRINT STYLES
+   ========================================================================== */
+
+/*
+   Hide the following elements on print
+   ========================================================================== */
+
+@media print {
+  .masthead,
+  .toc,
+  .page__share,
+  .page__related,
+  .ads,
+  .page__footer {
+    display: none;
+  }
+}