Description:
------------
It should works exactly like the `clone`, but with some features.

    // Usage.
    clone($user)->find(1);

    // Currently (too verbose):
    $userClone = clone $user;
    $userClone = $userClone->find(1);

    // __clone() reinforcement: callback that can 
    // - get/set private/protected attributes or 
    // call private/protected methods.
    clone($user, function ($baseObject) use ($externalData) {
        $this->privateAttribute = $baseObject->privateAttribute + $externalData;
    });

Signature (pseudo-code):

    function clone ($object, callable $callback = null) {
        assert(is_object($object));
     
        if (!$callback) return clone $object;

        // __clone() is called here.
        $clone = clone $object; 

        // Pass $clone as $this, and $object as first parameter.
        // Before call(), __clone() is called.
        $callback->call($clone, $object);

        return $clone;
    }