Adds zmqpp::actor, this class is similar to CZMQ zactor, that is it provide an easy way to spawn a thread an to communicate with it. Adds a zmqpp::signal enumeration that is used to send signal to socket (for interthread synchronization). zmqpp::socket and zmqpp::message have new methods to deal with zmqpp::signal
Merge pull request #51 from xaqq/actor_pr

zmqpp::actor