Simple utility to convert .s3g files to Wavefront .obj files for preview purposes

This is copied / pasted from s3g-decompiler.py. The two tools should be merged somehow to not duplicate the logic, but until then I figured I'd share this tool as it has come in handy for me to debug my .s3gs before sending them to print. Let me know if you'd like help merging the tools together before accepting the pull request and your recommended approach.