logger: use shared_ptr

include/opendht/dht.h

include/opendht/dht_interface.h

include/opendht/dht_proxy_client.h

include/opendht/dhtrunner.h

include/opendht/network_engine.h

include/opendht/network_utils.h

include/opendht/securedht.h

src/dht.cpp

src/dht_proxy_client.cpp

src/dhtrunner.cpp

src/log.cpp

src/network_engine.cpp

src/network_utils.cpp

src/securedht.cpp