Added array_undot function

This function converts an array with dotted keys to an associative array. Not sure if it's the best name, but hopefully some of you find the helper useful in some way.

Example:
```
$array = array('developer.name' => 'John Smith', 'developer.age' => 25, 'developer.address.number' => 123, 'developer.address.street' => 'Fake St');
$undottedArray = array_undot($array);
// $undottedArray is now array('developer' => array('name' => 'John Smith', 'age' => 25, 'address' => array('number' => 123, 'street' => 'Fake St')))
```