pdfs on PMC result list

pdf attachments were not showing up in the result lists of PMC, added them, and also did some cleanup and refactoring.

is there a way to have a real test for a result list? the test added just shows that the page would return multiple...
just in case add `[1]` before `/@href`. Better yet, grab the actual URL (for proxies and whatnot), so `ZU.xpath(.../a)[0]` then get `.href` of that if it exists)