Remove init.d script for upstart-managed dnsmasqs

If we manage dnsmasq using upstart on ubuntu, we should remove the
possibility of somebody messing things up by running the old init.d
script. Ubuntu provides a shim in /lib/init/upstart-job which forwards
any requests to your init.d script to upstart instead.
Update README

General tidy up, and also document the new class parameters
Merge pull request #4 from alphagov/remove-initd-script

Remove initd script