Implement disconnect

[fantix]

No description provided.

[cjdsellers]

Could you please provide some more description.

[Alexei-Kornienko]

Currently you have a connect method that allows you to connect to some endpoint. And you also have a close method that is used to completely shutdown the socket. So it may be the need to implement disconnect method that will be used to cancel a connect call and leave other parts intact. It may also be related to automatic reconnects cause it's required by ZeroMQ spec and it's currently missing

[Dav1d23]

Hello, I'm trying to implement a server using this crate, and I actually fall short of "files" since it seems that the server keeps tasks open even when the client connection is closed. I pushed some test code in https://github.com/Dav1d23/zeromq_connection_not_closed, is it because of the problem stated in this issue?

Thanks!

Edit: I just wanted to add that the provided code is what I've found to be a minimal example: you can run the 2 provided binary, open the tokio-console on the server and check that there are many tasks not "freed" even when the clients are disconnected completely.