Fix some issues with relative URLs on Github Pages.

docs/templates/shared/_head.liquid

@@ -1,12 +1,12 @@
 <head>
   <meta charset=UTF-8>
   <title>{{headline}} | jq</title>
-  <link rel="stylesheet" href="/bootstrap/css/bootstrap.css" type="text/css">
-  <link rel="stylesheet" href="/css/base.css" type="text/css">
+  <link rel="stylesheet" href="{{root}}/bootstrap/css/bootstrap.css" type="text/css">
+  <link rel="stylesheet" href="{{root}}/css/base.css" type="text/css">
   <!--[if IE]>
     <script src="http://html5shiv.googlecode.com/svn/trunk/html5.js"></script>
   <![endif]-->
   <script src="//ajax.googleapis.com/ajax/libs/jquery/1.8.1/jquery.min.js"></script>
-  <script src="/bootstrap/js/bootstrap.js"></script>
+  <script src="{{root}}/bootstrap/js/bootstrap.js"></script>
 
 </head>

docs/templates/shared/_header.liquid

@@ -7,12 +7,12 @@
         <span class="icon-bar"></span>
         <span class="icon-bar"></span>
       </button>
-      <a class="brand" href="/">jq</a>
+      <a class="brand" href="{{root}}/">jq</a>
       <div class="nav-collapse collapse">
         <ul class="nav">
           {% for item in navigation %}
             <li {% if item.permalink == permalink %} class="active" {% endif %}>
-              <a href="{{item.permalink}}">{{item.name}}</a>
+              <a href="{{root}}{{item.permalink}}">{{item.name}}</a>
             </li>
           {% endfor %}
           <li><a href="https://github.com/stedolan/jq/issues">Issues</a></li>