Things to do:

- Optimizing tarballs?
- gifrecolor?
- jpgstrip?

- scripts/zip2tarcat does not run under Python 3:

    $ python3.7 scripts/zip2tarcat test.zip > test.tar

    Traceback (most recent call last):
      File "./zip2tarcat", line 80, in <module>
        tarf.close()
      File "/usr/lib/python3.6/tarfile.py", line 1740, in close
        self.fileobj.close()
      File "/usr/lib/python3.6/tarfile.py", line 467, in close
        self.fileobj.write(self.buf)
    TypeError: write() argument must be str, not bytes
