Description:
------------
Idea: an easy to use parallel processing function for arrays (or any iterable 
data structure).

Example:

<?php
$arr = array(1, 2, 3, 4);
array_process_parallel($arr, function($a) { return $a+5; });
?>

Now $arr would contain the following: [6, 7, 8, 9].
The values are written back to $arr. The parameter is called by reference.

Also a array_parallel_reduce would be nice.

Test script:
---------------
$arr = array(1, 2, 3, 4);
array_process_parallel($arr, function($a) { return $a+5; });

Expected result:
----------------
[6, 7, 8, 9]