Zof

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- Rename to zof.
- Add close() method to Datapath class for hanging up.
- Change default log format.
- Metrics app now initiates on prestart event.
- Add zof.demo.hub module.

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- Add the set_apps function.
- Datapath service adds 'datapath' property to all message events.
- Add 'src' and 'dst' read-only properties to PktView.
- Add 'port_up' metric.
- Support slash notation in IPV6_ND_TARGET, IPV6_ND_SLL, and IPV6_ND_TLL fields.

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- Fix bug in datapath service.

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- Initial release.