docstrings

include/grpc++/alarm.h

include/grpc++/channel.h

include/grpc++/impl/codegen/completion_queue.h

include/grpc++/impl/codegen/core_codegen_interface.h

include/grpc++/impl/codegen/grpc_library.h

include/grpc++/impl/grpc_library.h

include/grpc++/security/credentials.h

include/grpc++/server.h

src/cpp/client/secure_credentials.cc

src/cpp/codegen/codegen_init.cc

src/cpp/common/core_codegen.h

src/cpp/common/grpc_library.cc