Shorter plugin initialization and set reset/clear form options through data attributes

[izziaraffaele]

With this pull-request you'll have 2 new small features:

• Shorter plugin initialization. For me it's really useful expecially when I have to use ajaxSubmit and I have to build the url dinamically or I have to get extra data. This feature works for both ajaxForm and ajaxSubmit.

$( '#form' ).on('submit',function(e){
     e.preventDefault();
     // get extra data or build url
     $(this).ajaxSubmit( url, data, dataType, function(response){
             //success callback function
     });
});

• You can use data attributes to set resetForm/clearForm options. Useful when you have general settings for most of the forms and you need an easy way to customize special forms while you are printing them out.

<form action="" method="POST" data-reset="true"></form>
<form action="" method="POST" data-clear="true"></form>

[kevindb]

This pull request was committed into the maintained fork of this plugin at 748a67c