Merge updates from debian/buster

CMake/CheckCxxTarget.cmake

CMake/FindSystemd.cmake

CMake/config.h.in

CMakeLists.txt

Dockerfile

README.md

apt-pkg/CMakeLists.txt

apt-pkg/acquire-item.cc

apt-pkg/acquire-item.h

apt-pkg/acquire-method.cc

apt-pkg/acquire-worker.cc

apt-pkg/contrib/configuration.cc

apt-pkg/contrib/fileutl.cc

apt-pkg/contrib/fileutl.h

apt-pkg/contrib/gpgv.cc

apt-pkg/contrib/hashes.cc

apt-pkg/contrib/md5.cc

apt-pkg/contrib/netrc.cc

apt-pkg/contrib/netrc.h

apt-pkg/contrib/strutl.cc