XPUB/XSUB sockets support

[thierry-tct]

Hello,

Is there any plan to implement support for XPUB/XSUB sockets anytime soon?

[cetra3]

I'd be open for someone to contribute a PR for those sockets, but don't otherwise have plans on implementing them.

[thierry-tct]

Alright, I will try to put some time aside to work on that, if that is okay