Add support for newer AAXC Audible Audiobook format
The older AAX format contains the actual decryption key, protected with a trivial account specific master key.
The new format, used by Audible since 2019, no longer embeds the decryption key.
The older AAX format contains the actual decryption key, protected with a trivial account specific master key.
The new format, used by Audible since 2019, no longer embeds the decryption key.