add yxml.forEach method - closes #421

src/types/YXmlFragment.js

@@ -404,6 +404,15 @@ export class YXmlFragment extends AbstractType {
     return typeListSlice(this, start, end)
   }
 
+  /**
+   * Executes a provided function on once on overy child element.
+   *
+   * @param {function(YXmlElement|YXmlText,number, typeof this):void} f A function to execute on every element of this YArray.
+   */
+  forEach (f) {
+    typeListForEach(this, f)
+  }
+
   /**
    * Transform the properties of this type to binary and write it to an
    * BinaryEncoder.