Use more appropriate structure for site navigation

Use the structure as documented in
http://v4-alpha.getbootstrap.com/components/navbar/#collapsible-content
- wrapping both the toggle and the navigation in a `<nav>`, using a
`<ul>` for the navigation items

docs/_includes/nav-home.html

@@ -24,22 +24,36 @@
   </nav>
   {% endcomment %}
 
-  <div class="clearfix">
-    <button class="navbar-toggler pull-xs-right hidden-sm-up" type="button" data-toggle="collapse" data-target="#bd-main-nav" aria-controls="bd-main-nav" aria-expanded="false" aria-label="Toggle navigation">
-      &#9776;
-    </button>
-    <a class="navbar-brand hidden-sm-up" href="{{ site.baseurl }}/">
-      Bootstrap
-    </a>
-  </div>
-  <div class="collapse navbar-toggleable-xs" id="bd-main-nav">
-    <nav class="nav navbar-nav">
-      <a class="nav-item nav-link {% if page.layout == "home" %}active{% endif %}" href="{{ site.baseurl }}/" onclick="ga('send', 'event', 'Navbar', 'Community links', 'Bootstrap');">Bootstrap</a>
-      <a class="nav-item nav-link {% if page.layout == "docs" %}active{% endif %}" href="{{ site.baseurl }}/getting-started/introduction/" onclick="ga('send', 'event', 'Navbar', 'Community links', 'Docs');">Documentation</a>
-      <a class="nav-item nav-link {% if page.title == "Examples" %}active{% endif %}" href="{{ site.baseurl }}/examples/" onclick="ga('send', 'event', 'Navbar', 'Community links', 'Examples');">Examples</a>
-      <a class="nav-item nav-link" href="{{ site.themes }}" onclick="ga('send', 'event', 'Navbar', 'Community links', 'Themes');">Themes</a>
-      <a class="nav-item nav-link" href="{{ site.expo }}" onclick="ga('send', 'event', 'Navbar', 'Community links', 'Expo');">Expo</a>
-      <a class="nav-item nav-link" href="{{ site.blog }}" onclick="ga('send', 'event', 'Navbar', 'Community links', 'Blog');">Blog</a>
-    </nav>
-  </div>
+  <nav>
+    <div class="clearfix">
+      <button class="navbar-toggler pull-xs-right hidden-sm-up" type="button" data-toggle="collapse" data-target="#bd-main-nav" aria-controls="bd-main-nav" aria-expanded="false" aria-label="Toggle navigation">
+        &#9776;
+      </button>
+      <a class="navbar-brand hidden-sm-up" href="{{ site.baseurl }}/">
+        Bootstrap
+      </a>
+    </div>
+    <div class="collapse navbar-toggleable-xs" id="bd-main-nav">
+      <ul class="nav navbar-nav">
+        <li class="nav-item active">
+          <a class="nav-item nav-link {% if page.layout == "home" %}active{% endif %}" href="{{ site.baseurl }}/" onclick="ga('send', 'event', 'Navbar', 'Community links', 'Bootstrap');">Bootstrap</a>
+        </li>
+        <li class="nav-item">
+          <a class="nav-item nav-link {% if page.layout == "docs" %}active{% endif %}" href="{{ site.baseurl }}/getting-started/introduction/" onclick="ga('send', 'event', 'Navbar', 'Community links', 'Docs');">Documentation</a>
+        </li>
+        <li class="nav-item">
+          <a class="nav-item nav-link {% if page.title == "Examples" %}active{% endif %}" href="{{ site.baseurl }}/examples/" onclick="ga('send', 'event', 'Navbar', 'Community links', 'Examples');">Examples</a>
+        </li>
+        <li class="nav-item">
+          <a class="nav-item nav-link" href="{{ site.themes }}" onclick="ga('send', 'event', 'Navbar', 'Community links', 'Themes');">Themes</a>
+        </li>
+        <li class="nav-item">
+          <a class="nav-item nav-link" href="{{ site.expo }}" onclick="ga('send', 'event', 'Navbar', 'Community links', 'Expo');">Expo</a>
+        </li>
+        <li class="nav-item">
+          <a class="nav-item nav-link" href="{{ site.blog }}" onclick="ga('send', 'event', 'Navbar', 'Community links', 'Blog');">Blog</a>
+        </li>
+      </ul>
+    </div>
+  </nav>
 </header>