Adds a11y landmarks

_includes/home-banner.html

@@ -1,8 +1,8 @@
-<header class="home-banner">
+<div class="home-banner">
   <h1>Liquid</h1>
   <p>Safe, customer facing template language for flexible web apps.</p>
   <p class="btn-row">
     <a href="https://github.com/Shopify/liquid/archive/master.zip" target="_blank" class="btn"><i class="icon fa fa-2x fa-arrow-circle-down" aria-hidden="true"></i>Download</a>
-    <a href="https://github.com/Shopify/liquid" target="_blank" class="btn" aria-hidden="true"><i class="icon fa fa-2x fa-github"></i>View on GitHub</a>
+    <a href="https://github.com/Shopify/liquid" target="_blank" class="btn"><i class="icon fa fa-2x fa-github" aria-hidden="true"></i>View on GitHub</a>
   </p>
-</header>
+</div>

_includes/sidebar.html

@@ -1,7 +1,7 @@
 <div class="sidebar">
-  <div class="sidebar__logo">
+  <header class="sidebar__logo">
     <a href="{{ "/" | prepend: site.baseurl }}">Liquid</a>
-  </div>
+  </header>
   <nav class="sidebar__nav"> {% assign sections = "basics, tags, filters" | split: ", " %}
 
     {% for section in sections %}