PS4 PKG support

[maxton]

We should add a PKG package format. Some thoughts on what's needed:

• [x] Find a library for AES-XTS or implement an AES-XTS decryption stream
• [x] Figure out PFSC format for inner pfs_image.dat
• [x] Find a library for the PFS compression
• [x] Determine a way to lookup keys on file system or programmatically set keys through the API
  • this is solved on the API side only, you have to put the key in a static variable