Add the debian subdirectory

This will make it easier for me to do PPA builds.  And the new Debian
packaging format makes it easy for them to replace upstream debian/
subdirs, AFAIU.

Note to self:

  cd ..
  pip install -d . gtimelog
  mv gtimelog-$VER.tar.gz gtimelog_$VER.orig.tar.gz
  cd gtimelog
  git checkout $VER
  debuild -i
  sudo dpkg -i ../gtimelog_$VER-*.all.deb
  # test
  debuild -i -S -k$GPGKEY
  dput ppa:gtimelog-dev/ppa ../../gtimelog_$VER-*.changes