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...
`"^https?://(www\.)?ncbi\.nlm\.nih\.gov/pmc/" (unless I'm missing a case where the host is different)