Look into supporting ZMQ::FFI backend

[zmughal]

• Use ->get or ->get_fd to retrieve socket file handle.

[JonnoFTW]

Will this upgrade be pushed to CPAN?

[zmughal]

I've been waiting on zeromq/perlzmq#44, but I'll go ahead now!

[zmughal]

Net-Async-ZMQ-0.002 is now headed to CPAN with these changes.