code: function keys (o) {
                      if(o === undefined || o === null) return [];
  
                      var keys = getKeys(o), idx;
                      if(libs.object.isArguments(o)) {
                          idx = keys.indexOf('length');
                          if(idx > -1) keys.splice(idx, 1);
                      }
                      return keys;
                  }
docs: Returns the object's keys.
  @param {Object} o The object to operate on.
  @returns {Array<String|Number>} The object's key set
  @function