Multi-version postgres-hll rules and control.in file

Right now the postgresql-hll seen in Debian unstable installs but one
version. I see you are the maintainer listed on packages.debian.org

I noticed some commented out lines in "debian/rules" that suggested at
some point someone tried to use "pg_buildext" but decided not to for
some reason.

I have need for the multi-version approach and cribbed and stripped
down what I could from plv8 and it seemed to work, and it is attached
for your consideration. I thought about doing a patch but realized
that the diff provides more noise than light and have instead included
a copy of "rules" "pgversions", and "control.in" instead.

Forgive me for any easy mistakes, I'm not an expert here.