zmq: remove crufts
zmq: refactor diet_string_set/diet_string_get with modified signature
remove now useless diet_arg_t structure and diet_parameter free function
zmq: remove useless empty strings
diet_string_set now sets an empty string by default
zmq: fix Socket::send method when we receive or not null-terminated strings
zmq: remove old tests from Proof-Of-Concept
zmq: tests refactoring
simplify string comparisons
simplify smart pointers use: <smart_ptr>.get()-> is equivalent to <smart_prt>-> (easier to read and one function call less)
zmq: refactor Server class using STL facilities and make code more readable