Req: Export Missing option

[bobpaul]

This suggestion came from reddit and was described as a diff export.

Story: As a user, I want to send my friends a pak file containing only the files that fail to download.

Idea
Stan has the entire mod cached already. Stan wants to play a mod with his friends, and from Stan's perspective, everything works great. But Stan's friends complain that some models and other resources aren't loading and they get errors.

Stan uses TTS-Manager to export "only missing". TTS-Manager attempts to download all resources in the mod.json file, and compares them to Stan's local cache. Any files that completely fail to download or differ from Stan's cache are added to the export from Stan's cache. Any files that successfully download and match Stan's cache are ignored.

Instead of sending his friends a 150MB *.pak file, Stan instead sends a 15MB *.diffpak file, which is small enough to directly attach to an email. Stan's friends use TTS-Manager to unpack it.

[cwoac]

So, I started on this last night. Fairly easy to code up (I've got it working in the CLI). but it seems that it is going to be functionally limited until I've done #33 from my testing so far.