Rewrite packaging to use d/<pkg> for staging packages and use more debhelper

Rewrite packaging to use d/<pkg> for staging packages and use more debhelper

With this change, packages are now staged in debian/<pkg> rather than
debian/tmp/<pkg>. This simplifies using debhelper a lot since the
debhelper tools assumes debian/<pkg> by default. The packaging now also
uses a few more debhelper tools for standard handling.

The primary delta from the previous debs with this commits are:

 1) dh_installchangelogs uses native packaging rules without a
    "changelog.Debian.gz" compat symlink. Given the package is
    considered a native package, the loss of the symlink seemed
    acceptable.

 2) dh_installchangelogs trims out very old changelog entries, which
    the original code did not. This delta is to be expected but still
    noisy in the diffoscope delta.

 3) The package now uses dh_compress, which has a different rule
    set for what files to compress. So far, this means more files
    in /usr/share/doc are now compressed.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>