Mark undocumented doclets as undocumented

To give other plugins access to doclets that are not part of
the API, we have to mark them undocumented instead of removing
them. They will be removed by JSDoc before publishing anyway.

apidoc/plugins/api.js

@@ -69,7 +69,7 @@ exports.handlers = {
         doclet.hideConstructor = true;
       } else {
         // Remove all other undocumented symbols
-        doclets.splice(i, 1);
+        doclet.undocumented = true;
       }
     }
   }