Fixed keyDownHandler and added new feature

Hi,

I added new feature for passing options to JQuery autocomplete in convenient way:

```coffee
    completer = new GmapsCompleter

    completer.autoCompleteInit
      country: "us"
      autocomplete:
        minLength: 4
        position: 
          my : "center top", 
          at: "center bottom-1"
          collision: "none"
```

This *autocomplete* object will be merged with default *source* and *select* functions and passed to JQuery autocomplete widget.

Also I fixed issues with *this* in keyDownHandler.