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...
same with this. see https://github.com/zotero/translators/blob/b581911a0789643b0b1658b5518e740be0260a45/Cambridge%20Journals%20Online.js#L26