the latest zerorpc code needs at least pyzmq 13

zerorpc 0.4.3 is incompatible with pyzmq 2.2.0.1.

How to reproduce:

    mkvirtualenv tmp
    pip install pyzmq==2.2.0.1
    pip install zerorpc
    zerorpc --server urllib --bind tcp://0.0.0.0:1234
    ...
    KeyError: '_msg_id_counter'

Upgrading to pyzmq 13.0 (or later) fixes the problem.

I think it's useful to upgrade the dependencies correctly, because people trying to upgrade zerorpc will break their existing install (since the current deps only specify pyzmq>=2.2.0.1).