extend .key() method can delegate binding if using jQuery or Zepto

This feature need jQuery or Zepto.
usage:
jwerty.key('ctrl+enter', function(){...}, '.element_currently_not_ exist');
jwerty.key('ctrl+enter', function(){...}, '.element_currently_not_ exist_too', '.wrap_element');

and we can use like this:
$('.wrap_element').jwerty('ctrl+enter', function(){});
$('.wrap_element').jwerty('ctrl+enter', '.element_currently_not_exist', function(){});