add: pipeline categorization by metadata key

examples/basic/layouts/base.html

@@ -7,6 +7,6 @@
         <title>{{- if .Title -}}{{ .Title }} | {{ else }}{{ end -}} My Blog</title>
     </head>
     <body>
-        {{- .Content -}}
+        {{ .Content }}
     </body>
 </html>

examples/basic/layouts/tag.html

@@ -0,0 +1,12 @@
+<h1>Tag #{{ .Category }}</h1>
+
+<p>Here are the posts with this tag</p>
+
+<ul>
+    {{ range .Items }}
+    <li>
+        <p>{{ .Metadata.Title }}</p>
+        <pre><code>{{ .Metadata.MatchResult }}</code></pre>
+    </li>
+    {{ end }}
+</ul>