Added callback to preprocess to allow holding up page rendering if waiting for data
Code cleanup to satisfy build process
Added option to ajax to include additional  xhrFields, e.g. add withCredentials = true;

Example usage:
```
var        options = {
                                url: 'someurl.php',
                                method: 'POST',
                                cache: true,
                                data: someObject,
                                xhrFields: {
                                    withCredentials: true
                                },
                                crossDomain: true
                            };

                        return $$.ajax(options);
```
Merge pull request #84 from gregkeys/master

Added callback to preprocess