logger: remove OPENDHT_LOG, rename to logger.h

CMakeLists.txt

configure.ac

include/opendht/dht_interface.h

include/opendht/dhtrunner.h

include/opendht/log.h

include/opendht/logger.h

include/opendht/network_engine.h

include/opendht/network_utils.h

include/opendht/peer_discovery.h

src/Makefile.am

src/compat/os_cert.cpp

src/compat/os_cert.h

src/dht.cpp

src/http.cpp

src/network_engine.cpp