fix #11: flattened keys in array are now correctly parsed

`Qs` can now parse:  

`anArray[0][a]=a&anArray[0][b]=b&anArray[1][a]=aa&anArray[1][b]=bb`  
to
```js
var data = {
  anArray: [
    { a: 'a', b: 'b' },
    { a: 'aa', b: 'bb' }
  ]
};
```