feat(attribute.js): add static of method

lib/attribute.js

@@ -6,9 +6,22 @@
  */
 class Attribute {
 
+    /**
+     * Wrap an Attribute to get access to utility functions
+     * @param {String} [key=undefined] key key of the attribute
+     * @param {String} [value=undefined] value value of the attribute
+     * @returns {Attribute} a new Attribute
+     */
+    static of(key, value) {
+
+        return new Attribute(key, value)
+    }
+
     /**
      * @constructor
-     * @param {string} key attributes key
+     * @private
+     * @description <b>Do not use this method directly. Use one of the static helper methods instead.</b
+     * @param {string} [key=undefined] key attributes key
      * @param {string} [value=undefined] value attributes value
      * @returns {Attribute} a new Attribute
      */