DVD-Audio: add still image integration

This will solve #23 by

1. Documenting asvs info structures
2. Implementing a read for asvs ifo structures
3. Exposing the audio_sv.vob stills by rewriting the openvob logic
4. Changing the decryption logic to allow switching between cpxm and css on the fly as vob tracks are encrypted with css in DVD-audio

This merge would help open up for a full implementation of DVD-audio, with menus and stills

I've gathered all of the AUDIO_SV.IFO files I have access to, there is currently no official specification for the ASVS, this is information gathered from what I have

There will be a zip file upload containing all of the AUDIO_SV.IFO xxd outputs I have, along with the unencrypted VOB's that exist (the vob's seem to be encrypted with css, this merge will need to include changes to dvdcss)

https://drive.google.com/file/d/1coXWp30wH7PIbRz8YRfAvlLjE3vB5OOn/view?usp=sharing