Zyre binding

Add the class ZMQZyre which is a binding of the libzyre. Zyre is an open-source framework for proximity-based peer-to-peer applications. Zyre is based on ZMQ and supported by iMatix.

The ZMQZyre class is add to the php extension if all library dependency are validate, if not this part of the code is disable automatically to avoid build error.
- libzyre == 1.x.x
- czmq >= 2.2.0

Checking for NULL?