Add a makefile for building debian packages
This allow building debian source package from sdist. This is cleaner than building from hg clone because we ensure to only include what's listed in sdist MANIFEST.in in upstream tarball.
The "deb-zip" target allow to build a zip for the source package, suitable as input of https://jenkins.intra.logilab.fr/job/pkg-from-dsc
The "deb" target build the binary packages using sbuild.