Added PDF embed

Hi Noahy,

I added the feature to embed PDFs. 

Here is the news post: http://www.question2answer.org/qa/33644/pdf-embed-now-possible-with-extended-q2a-embed-plugin

You might want to include it into your code.

I will inform Scott to change the core qa-blob.php, because it needs a change to deliver PDFs as inline and not as attachment.

Greetings,
Kai
