Simple changes to track new ocaml-zmq API
1st steps towards an internal ZMQ binding

Binds to ZMQ using ctypes.

Pretty much direct copy of lwt-zmq (which is quite simple in itself)

Completely different build system as we need to make all sorts of dlls.

It can run a couple of expressions so it's getting there.
include new zmq bindings
fix installation

...and raise posix errors for lwt_zmq
zmq3/4 compatibility
Merge pull request #18 from andrewray/zmq4

Zmq