Release 0.7
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* Introduced enumeration types for several ZMQ constants for type-safety.
* Added a new polling based implementation that works for all ZMQ communication protocols.
* Dropped support for REQ-REP protocol for old 'QSocketNotifier' based implementation.
* Added some more convenience methods to 'ZMQSocket' class.
* Old and new socket implementations now emit a signal with a received message as parameter.

