Zapatec DHTML Form Widget - Send files to server using AJAX

This demo uses the winxp theme.
This demo shows how to send files to server without refreshing the whole page
You must use combination of asyncSubmitFunc and serverCallback config options
asyncSubmitFunc defines what function will be called after form submit. You can use it for hiding form, for example.
serverCallback determines parameter name, that will be sent to server. This parameter will hold JavaScript function name that must be called to finish form submit.
On server-side you must process form submit, validate fields, store files. As response your script must respond with the following page (example for PHP):
```
<html><body><script type='text/javascript'>
<?= $_POST["callback"] ?>(...);
</script></body></html>
```
Instead of "..." you need to put JSON response. Its format is described in Submit form to server using AJAX demo.
Warning! If server won't respond with such page - asyncSubmitFunc function won't be called and errors won't be displayed!
Current demo has field for entering files. Using zpFormMultiple feature user can send multiple files to server. Server-side script validates all input fields, creates array with errors and passes it back to client. Also it calculates number of sent files and their total size.