/*
   * Add a string property as key/value pair (an 'add_property' analogue for adding array items)
   * * Input parameters to 'invoke'd methods are represented as ClientOption properties
   *
   * call-seq:
   *   options.add_property( "Key", "Value" )
   *
   */
  void add_property_array_item(const char *key, const char *value)