Planet Arch Linux migration

The software behind planet.rgdwk.mwscdfr.qzz.io was implemented in Python 2 and is no longer maintained upstream. This functionality has now been implemented in rgdwk.mwscdfr.qzz.io's archweb backend which is actively maintained but offers a slightly different experience.

The most notable changes are the offered feeds and the feed location. Archweb only offers an Atom feed which is located at here.