#463, move gh-pages to docs folder

docs/_includes/banner.html

@@ -0,0 +1,9 @@
+<div class="site-banner">
+    <div class="wrapper vertical-align-middle">
+        <p class="tag-line">
+            Read and write spreadsheets
+            <br />
+            <strong>quickly</strong> and <strong>at scale</strong>
+        </p>
+    </div>
+</div>