Calling patool directly

[miAndreev]

Hi, I saw that patool isn't called from python. Is there a reason to call it in a sub process? I can provide a pull request.

[ponty]

Reasons:

1. Historic: patool had only CLI interface in the past.
2. License: This lib is BSD, but patool has GPLv3 license: https://github.com/wummel/patool/blob/master/COPYING If we add the direct Python call, then pyunpack can not be used in non GPL projects as it is now.