Add support to nested objects serializer

[hdbreaker]

This change allow serialize nested objects, and simple objects without need use phpobject hook, but for mantain legacy versions use, i have kept the code of phpobject hook

if isinstance(obj, phpobject):
return b'O' + _serialize(obj.name, True)[1:-1] + _serialize(obj.php_vars, False)[1:]
else:
nested or python object code...

i attach my example code:
POISerializer.zip

[hdbreaker]

I add some changes more, now the code if able to serialize and unserialize nested objects.
I write this changes couse i need to serializate nasted objects to made a demo of how exploit the security bug of PHP Object Injection
POISerializer.zip