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/_mixins.scss

@@ -0,0 +1,53 @@
+/* ==========================================================================
+   MIXINS
+   ========================================================================== */
+
+%tab-focus {
+  /* Default*/
+  outline: thin dotted $warning-color;
+  /* Webkit*/
+  outline: 5px auto $warning-color;
+  outline-offset: -2px;
+}
+
+/*
+   em function
+   ========================================================================== */
+
+@function em($target, $context: $doc-font-size) {
+  @return ($target / $context) * 1em;
+}
+
+
+/*
+   Bourbon clearfix
+   ========================================================================== */
+
+/*
+  * Provides an easy way to include a clearfix for containing floats.
+  * link http://cssmojo.com/latest_new_clearfix_so_far/
+  *
+  * example scss - Usage
+  *
+  * .element {
+  *   @include clearfix;
+  * }
+  *
+  * example css - CSS Output
+  *
+  * .element::after {
+  *   clear: both;
+  *   content: "";
+  *   display: table;
+  * }
+*/
+
+@mixin clearfix {
+  clear: both;
+
+  &::after {
+    clear: both;
+    content: "";
+    display: table;
+  }
+}