Problem: no documentation for new zmq_poller_* APIs

[bluca]

It's still in DRAFT state, but it would be good to have at least an initial draft of the documentation.

@minrk @somdoron ping :-)

[somdoron]

I will try to find time next week to add docs...

[bluca]

Thanks! It's not super-urgent given it's still draft, so no rush :-)