Allow setting and getting socket options

[jasonroelofs]

With the release of ZeroMQ 4, there are ever more options that can be set on a socket. Specifically in my case, the security options. This PR adds #set and #get to sockets which just proxy the arguments directly down to the ffi-rzmq handler for the socket. Celluloid doesn't have to care about types, that's handled deeper down.

[jasonroelofs]

The build is failing because of changes made in Celluloid 0.16 (not out yet) and this project pulls in Celluloid from master via bundler. Tests pass fine on Celluloid 0.15.

[tarcieri]

Seems good. By "security options" do you mean CurveZMQ? That is definitely something I'm interested, and while I've been tracking the protocol changes vs CurveCP, I haven't done much digging into the actual implementation.

I would like to get the tests passing with Celluloid 0.16 first, then maybe we can rebase this and merge when the tests pass again?

[jasonroelofs]

Yep! Curve is delightfully easy to set up and use. I put together a quick example here: https://github.com/chuckremes/ffi-rzmq/blob/master/examples/repreq_over_curve.rb. And sure, I'll keep an eye on things and keep this branch up-to-date.

[tarcieri]

Wanted to give this more scrutiny because it's security-related, but this change looks rather trivial. Also the build failures seem to be unrelated.

[tarcieri]

Seems good, thanks!