Add support for draft socket types

[staticfloat]

These APIs are not yet fully stable, so using them across ZMQ versions is not guaranteed to work. Within a ZMQ version, they should be more or less functional however, so let's expose them but within a Draft module that signals to the user a whiff of caveat emptor.

Associated Yggdrasil PR enabling the draft code within libzmq: https://github.com/JuliaPackaging/Yggdrasil/pull/1128

[staticfloat]

I've marked this as draft because Socket() fails upon trying to call getsockopt(ZMQ_FD) until https://github.com/zeromq/libzmq/issues/3953 is resolved.