[4.2] Arr method to convert dot-notation keys in flat array to associative array

Adding method to Arr Helper that converts a one-dimensional array with keys that are written in dot notation into a multidimensional associative array.

From:

	array(
		'levelOne' => 1,
		'levelTwo.someKey' => 2,
		'levelTwo.anotherKey' => 3,
		'levelThree.moreKey.withMoreDepth' => 4,
		'levelThree.moreKey.andAssigningToSameDepthKey' => 5,
	)

to:

	array(
		'levelOne' => 1,
		'levelTwo' => array(
			'someKey' => 2,
			'anotherKey' => 3,
		),
		'levelThree' => array(
			'moreKey' => array(
				'withMoreDepth' => 4,
				'andAssigningToSameDepthKey' => 5,
			)
		)
	)
Please add an `@return` annotation.