Update ZMQ links

[Peque]

Which now redirect to HTTPS.

See:

$ ag zeromq.org
docs/source/about.rst
19:- Message passing is implemented using `ØMQ <http://zeromq.org/>`_, and in
21:- `ØMQ <http://zeromq.org/>`_ allows for **efficient**, **asynchronous**
37:`ØMQ guide <http://zguide.zeromq.org/page:all>`_.
62:   and flexible `ØMQ <http://zeromq.org/>`_ library.
108:#. `ØMQ <http://zeromq.org/>`_ is used with the

docs/source/considerations.rst
26:`ØMQ guide <http://zguide.zeromq.org/page:all>`_.
48:`ØMQ guide <http://zguide.zeromq.org/page:all>`_.

docs/source/index.rst
19:osBrain uses `ØMQ <http://zeromq.org/>`_ for efficient and flexible message

README.rst
12:osBrain uses `ØMQ <http://zeromq.org/>`__ for efficient and flexible

[sgaist]

Hi,

I can take on this one :-)

[Peque]

@sgaist Great! :blush: