Py-pf

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- Updated to OpenBSD 7.4

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- Switching to Python 3 on the main branch
- Tested on OpenBSD 7.0

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- Tested on OpenBSD 6.5

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- Updated to OpenBSD 6.4

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- Updated to OpenBSD 6.3 (many thanks to
[Jasper Lievisse Adriaanse](https://github.com/jasperla) for his contribution)
- Support for syncookies was added to the `PacketFilter` class through 3 new
methods:
- `PacketFilter.get_synflood_watermarks()`
- `PacketFilter.set_synflood_watermarks()`
- `PacketFilter.set_syncookies()`
- Added a new `PFThreshold` class for `max-pkt-rate` thresholds
- Added a new `PFDivert` class to represent divert sockets

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- Updated to OpenBSD 6.2 (many thanks to
[Nathan Wheeler](https://github.com/nahun) for his contribution)
- Some little changes were made to the queueing part to integrate flows:
- a new `FlowQueue` object was created
- `PFQueue` objects have a new `flowqueue` attribute
- HFSC_* constants have been replaced with PFQS_* constants
- `PFStatus.since` now contains the number of seconds after machine uptime that
Packet Filter was last started or stopped (not anymore since the epoch).