Alter Autocomplete's source before request

Hi!

this module is awesome, because let's you deal with very complex situations, but there's no easy way to alter the source function parameters which are request and response.
For example, let's say you have an exposed filter with a select which filters the results of the autocomplete and the search at the same time.
With this patch you can implement an event, something like these:

$form = /* get the form element */
$form.on('searchautocompletesource', function (event, request, response) {
  var subhomeValue = $subhomeSelect.val();
  if (subhomeValue !== 'All') {
    request.subhome = subhomeValue;
  }
});

and with that we added a new parameter at the request callback of the autocomplete:
/search/autocomplete?term=quantum&subhome=physics


*In pair with @lucas.constantino