deckard: setup.py metadata overhaul

Version 3.0 reflects that we dropped support for Python 2.
All the other metadata were updated as well.

(Version 2.y could be the new parser but I forgot to update
the setup.py back then.)
7 jobs for rfc5011 in 1 minute and 16 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #36759
docker linux amd64
test:comparative:kresd

00:01:04

passed #36760
docker linux amd64
test:latest:kresd

00:01:16

passed #36756
docker linux amd64
test:pep8

00:00:27

passed #36757
docker linux amd64
test:pylint

00:00:59

passed #36762
docker linux amd64
test:sanity:pdnsrecursor

00:00:41

passed #36761
docker linux amd64
test:sanity:unbound

00:00:40

passed #36758
docker linux amd64
test:unittests

00:00:35