Only document olx properties marked as part of the API

And mark all olx properties with @api.  The stability level will be used to determine what can change between minor releases.

apidoc/plugins/typedefs.js

@@ -28,6 +28,10 @@ exports.handlers = {
   newDoclet: function(e) {
     var doclet = e.doclet;
     if (doclet.meta.filename == 'olx.js') {
+      // do nothing if not marked @api
+      if (!doclet.stability) {
+        return;
+      }
       if (doclet.kind == 'typedef') {
         lastOlxTypedef = doclet;
         olxTypes[doclet.longname] = [];