debian: Add a gbp.conf to start using git-buildpackage
On Bdale Garbee's recommendation I'm switching from gitpkg, (which
constructed a source tree but still required me to go run debuild), to
git-buildpackage. I hadn't originally used git-buildpackage because it
didn't seem to work without a configuration file, (where gitpkg was
fine).
Bdale was kind enough to point me to his fw/altos source at
git.gag.com where I found an example gpb.conf file as well as a target
in debian/rules to automatically update debian/changelog with the new
version number.