add propertychange handlder ,and structure change

here is some changes

1. I added a propertychange listener to handle the placeholder attribute change ,so when the attribute change , we can change the input value imidately
2. the updateplaceholder function and the createplaceholder function are almost same, and updatePlaceholder doesn't process the form submit for new added input element, so I merge the two function to one
3. sometimes, I don't wan't use the refresh to process the new input element which added after page loaded,I want a function just attach  the new input . so I add "attach" method

in addition， I don't think refresh method has meaning any more, except in the browser don't support properychange event. could you think about it?