Nest output formats

Per #162 (comment)

Signed-off-by: Roger Sheen <roger@infotexture.net>

toc.ditamap

@@ -12,7 +12,7 @@
       <navtitle>Release Notes</navtitle>
     </topicmeta>
   </topicref>
-  
+
   <topicref keyref="installing-client" locktitle="yes">
     <topicmeta>
       <navtitle>Installing DITA-OT</navtitle>
@@ -44,40 +44,46 @@
       <topicref keyref="building-with-ant"/>
       <topicref keyref="creating-an-ant-build-script"/>
     </topicref>
-    <topicref keyref="AvailableTransforms"/>
-    <topicref keyref="dita2eclipsehelp">
-      <topicref keyref="parameters-base"/>
-      <topicref keyref="parameters-base-html"/>
-      <topicref keyref="parameters-eclipsehelp"/>
-      <topicref keyref="generate-copy-outer"/>
-    </topicref>
-    <topicref keyref="dita2html5">
-      <topicref keyref="parameters-base"/>
-      <topicref keyref="parameters-base-html"/>
-      <topicref keyref="parameters-html5"/>
-      <topicref keyref="generate-copy-outer"/>
-    </topicref>
-    <topicref keyref="dita2htmlhelp">
-      <topicref keyref="parameters-base"/>
-      <topicref keyref="parameters-base-html"/>
-      <topicref keyref="parameters-htmlhelp"/>
-      <topicref keyref="generate-copy-outer"/>
-    </topicref>
-    <topicref keyref="dita2xhtml">
-      <topicref keyref="parameters-base"/>
-      <topicref keyref="parameters-base-html"/>
-      <topicref keyref="parameters-xhtml"/>
-      <topicref keyref="generate-copy-outer"/>
-    </topicref>
-    <topicref keyref="dita2pdf">
-      <topicref keyref="parameters-base"/>
-      <topicref keyref="parameters-pdf"/>
-    </topicref>
-    <topicref keyref="dita2tocjs">
-      <topicref keyref="parameters-base"/>
-    </topicref>
-    <topicref keyref="dita2troff">
-      <topicref keyref="parameters-base"/>
+    <topicref keyref="AvailableTransforms" locktitle="yes">
+      <topicmeta>
+        <navtitle>Output formats</navtitle>
+      </topicmeta>
+      <topicref keyref="dita2pdf">
+        <topicref keyref="parameters-base"/>
+        <topicref keyref="parameters-pdf"/>
+      </topicref>
+      <topicref keyref="dita2html5">
+        <topicref keyref="parameters-base"/>
+        <topicref keyref="parameters-base-html"/>
+        <topicref keyref="parameters-html5"/>
+        <topicref keyref="generate-copy-outer"/>
+      </topicref>
+      <topicref keyref="dita2eclipsehelp">
+        <topicref keyref="parameters-base"/>
+        <topicref keyref="parameters-base-html"/>
+        <topicref keyref="parameters-eclipsehelp"/>
+        <topicref keyref="generate-copy-outer"/>
+      </topicref>
+      <topicref keyref="dita2htmlhelp">
+        <topicref keyref="parameters-base"/>
+        <topicref keyref="parameters-base-html"/>
+        <topicref keyref="parameters-htmlhelp"/>
+        <topicref keyref="generate-copy-outer"/>
+      </topicref>
+      <!-- Markdown -->
+      <!-- NormDITA -->
+      <topicref keyref="dita2tocjs">
+        <topicref keyref="parameters-base"/>
+      </topicref>
+      <topicref keyref="dita2troff">
+        <topicref keyref="parameters-base"/>
+      </topicref>
+      <topicref keyref="dita2xhtml">
+        <topicref keyref="parameters-base"/>
+        <topicref keyref="parameters-base-html"/>
+        <topicref keyref="parameters-xhtml"/>
+        <topicref keyref="generate-copy-outer"/>
+      </topicref>
     </topicref>
   </topicref>
   <topicref keyref="parameters">