Changes:
- [change][major] Use COBS encoding for the packet list.
- [change][major] Encode packet sizes as `u16` instead of `u32`.
- [add][minor] Linux: Allow creating the tunnel interfaces in a named netns.
- [add][minor] Make the maximum payload size over the serial line configurable.
- [fix][minor] Refuse to allocate buffer space for excessively large payloads.
- [fix][minor] Check if CLI provided prefix lengths are valid for their address family.
- [fix][minor] Fix the default poll timeout for the `local` CLI command.
- [add][minor] Improve the README.