[Feature Request] Implement compression utils for various file formats

[hyoretsu]

This is something that other compression programs don't do, so it'd be a huge plus for the project. Basically, I read somewhere that compression doesn't work all that well in file formats that are already compressed, like MP3, PNG, JPG, etc. I tried to test that by compressing 19 MP3's, I only had a 2% decrease in storage usage.

So we could add pre-processors for those files, to (losslessly) compress even further. There's: PNGOUT.exe, OptiPNG and DeflOpt (also works for ZIP and GZIP on "deflate") for .png jpegoptim, packJPG for .jpg

[Artoria2e5]

First, this overlaps with #303.

Second, what you ask for is not going to pass any checksum. It's lossless to the underlying data, mostly, but not to the file being compressed. You gotta live with that.