chore(docs): enable page ordering by @sortOrder tag

docs/config/index.js

@@ -22,7 +22,8 @@ module.exports = function(config) {
   ]);
 
   config.append('processing.tagDefinitions', [
-    require('./tag-defs/tutorial-step')
+    require('./tag-defs/tutorial-step'),
+    require('./tag-defs/sortOrder')
   ]);
 
   config.append('processing.defaultTagTransforms', [

docs/config/processors/pages-data.js

@@ -119,13 +119,20 @@ var navGroupMappers = {
     })];
   },
   pages: function(pages, area) {
-    return [getNavGroup(pages, area, 'path', function(page) {
-      return {
-        name: page.name,
-        href: page.path,
-        type: 'page'
-      };
-    })];
+    return [getNavGroup(
+      pages,
+      area,
+      function(page) {
+        return page.sortOrder || page.path;
+      },
+      function(page) {
+        return {
+          name: page.name,
+          href: page.path,
+          type: 'page'
+        };
+      }
+    )];
   }
 };
 

docs/config/tag-defs/sortOrder.js

@@ -0,0 +1,6 @@
+module.exports = {
+  name: 'sortOrder',
+  transforms: function(doc, tag, value) {
+    return parseInt(value, 10);
+  }
+};