Implement .pk3 exporting; string truncating
- Uses the https://github.com/kuba--/zip library (referred to as "zip"), itself based on miniz.
- Replaces the ability to export to .wad altogether.
- To this end, lump.c and lump.h from Lumpmod were removed from the program.
- Skin graphics lumps, as well as the S_SKIN soc file, are located in "skins/[charactername]/". Sounds are in "sounds/skins/[charactername]/"
Also implements string truncating. See specific commit for more info.