added possibility to disconnect.
added possibility to disconnect.

chenwenbin928/cppzmq,michele-brambilla/ConfigurationService,caidongyun/cppzmq,zeromq/cppzmq,jens-auer/cppzmq,eburkitt/cppzmq,bsn069/cppzmq,K0n63n/cppzmq,cmcmurrough/cppzmq,michele-brambilla/ConfigurationService,michele-brambilla/ConfigurationService,michele-brambilla/ConfigurationService,virtdb/cppzmq,michele-brambilla/ConfigurationService,zeromq/cppzmq