Add VPK parsing functionality

[statecouncil]

Is your feature request related to a problem? Please describe.
Mapping work on TF2 can involve large amount of custom assets. While there are tricks to reduce game loading times in other ways, the by far most effective way is to pack any mounted assets into VPKs, which Source can load much more quickly. The main disadvantage of this method is that this stops Compilepal from detecting and packing individual assets when compiling for publication.

Describe the solution you'd like
Allow Compilepal to parse VPKs either by default or via a PACK parameter and automatically extract and include found assets, just like it does with loose files.

Describe alternatives you've considered
As mentioned, the alternative is to keep a large amount of loose files, which brings its own problems.

Additional context
I am currently working on a large "Mapping Starter Pack" for TF2 which will include a handful of VPKs modules that can be swapped in and out by mappers, similar to the Mastercomfig CFG packs. I would prefer not having to ask novice mappers how to pack/unpack VPKs as well as familarize themselves with the file structures before they're even able to start hammer. If I can just tell them to throw whatever VPKs they need into tf/custom/, it would lower the entrance barrier a little.

Cheers!