A slight fix for the Penny Arcade plugin

I'm one of the people who arrived at TT-RSS from GReader (and enjoying it so far).

The changes in this pull request modify the af_pennyarcade plugin to retrieve the full text of news posts. It uses the simplest method of doing this, basically just pasting the relevant DOM subtree as the article content without any further processing.

It's in a "works for me" state, obviously.