function createNormalRu( $rb, $rt, attr ) {
  var $ru = $.create( 'h-ru' )
  var $rt = $.clone( $rt )
  var attr = attr || {}
  attr.annotation = 'true'

  if ( Array.isArray( $rb )) {
    $ru.innerHTML = $rb.map(function( rb ) {
      if ( typeof rb === 'undefined' )  return ''
      return rb.outerHTML 
    }).join('') + $rt.outerHTML
  } else {
    $ru.appendChild( $.clone( $rb ))
    $ru.appendChild( $rt )
  }

  $.setAttr( $ru, attr )
  return $ru
}
Create and return a new `<h-ru>` element
in Zhuyin form