This update for zypper-keys-plugin fixes the following issues:

zypper-keys-plugin:
- Version 0.5.0
- Relicense to GPL3
- Add release script
- Require pytz

- Version 0.4.0
- Better doc in --help
- Show help and list keys if no args are given

zyppkeys:
- Version 0.5.0
- Relicense to GPL3
- Add release script
- Require pytz

- Version 0.4.0
- Switch to setuptools
- Show key help and list keys when called without args
- Add some more documentation via argparse
- Handle http errors when downloading keys
- Add readme examples