Single list of packages
Single list of packages

List packages and the kind of repo to pull from in one place. Read out
the pieces rather than duplication the info. Factor out the update
function for reuse so that exisiting exordium-extra-packages will work.

dvamin/dot.emacs,steve-downey/dot.emacs,philippe-grenet/exordium,jbibollet/exordium,psipika/exordium,pkryger/exordium,fcassirer/dot.emacs