Things left to do:
 * automate creating the orig.tar.xz though this should be coordinated with
   upstream. Currently these commands can be used to create it:

   VERSION=0.3.1
   git archive --format tar.gz --prefix=voctomix-$VERSION.orig/ -o ../voctomix_$VERSION.orig.tar.gz origin/master
   gunzip ../voctomix_$VERSION.orig.tar.gz
   xz ../voctomix_$VERSION.orig.tar

 * Not sure whether this should go into a new upstream Makefile or simply
   become a make-orig-tar-xz target…
