vpkpp: [CSO2 & TFO] PKG support

[begin-theadventure]

Describe Your Suggestion

Counter-Strike: Online 2's and Titanfall Online's proprietary archive format PKG.

There's a Qt GUI tool "UnCSO2" that supports this format, but it has been abandoned.
It uses the libuncso2 library as a backend.
For the library using this fork would probably be best.

EDIT: Since then both projects have been forked and updated:
https://github.com/harmonytf/UnCSO2
https://github.com/harmonytf/libuncso2