Merge pull request #127 from vyskocilm/master

Problem: codec headers reffer to czmq types
Problem: unconditionally using "czmq.h" and never considering the
library

Solution: check if "czmq.h" exists in projects context otherwise use
library.
Merge pull request #128 from sappo/master

Problem: unconditionally using "czmq.h" and never considering the library