Enable passing options to jQuery autocomplete initializer for inputs initialized by id selector

The javascript extension of jQuery autocomplete didn't allow to pass options to the autocomplete initializer.
I needed to specify a different position for the autocomplete widget, now it can be done like this:
```javascript
$('#input_id).railsAutocomplete({
    position: { my: "right bottom", at: "right top", collision: "flip" }
});
```
It currently works only for autocomplete inputs initialized by an id selector. So it doesn't influence the default initializer:
```javascript
jQuery("input[data-autocomplete]").railsAutocomplete();
```