Add make-release-tarball.sh

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Remove unnecessary #!/usr/bin/python3 headers in modules

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
setup.py: Add canonical download URL

Signed-off-by: Andy Lutomirski <luto@amacapital.net>