Make protected properties & methods inside Zip Class

[andreacivita]

Hi, i was trying to use this class and I need to extend it to add some features related to my business logic.

I see that inside ZanySoft\Zip\Zip class, a lot of properties and methods are setted to private. This behaviour prevents me from extending class.

Is it possible to change all private to protected?

If necessary, I can submit a PR with these changes