Add support for APFS Fillesystem

[shiren00]

We would appreciate it if anyone with additional materials or actual dump files related to this could share them :D
tsk_recover supports this.

• https://en.wikipedia.org/wiki/Apple_File_System
• https://developer.apple.com/support/downloads/Apple-File-System-Reference.pdf

[devttys0]

WIP: https://github.com/ReFirmLabs/binwalk/tree/apfs_support

[devttys0]

APFS support is functional and merged into the master branch.

Note that tsk_recover was not able to actually extract any of the APFS images that I created (using both Linux utilities and the OSX disk manager on a MacBook). The latest version of 7zip does work though, and has been added as a new external dependency.

[shiren00]

Thank you very much!!