Lightweight PSR-0 compliant autoloader

autoloader.php

<?php

spl_autoload_register(function ($className) {
    $fileParts = explode('\\', ltrim($className, '\\'));
    if (false !== strpos(end($fileParts), '_'))
        array_splice($fileParts, -1, 1, explode('_', current($fileParts)));
    require implode(DIRECTORY_SEPARATOR, $fileParts) . '.php';
});