Primo: make data extraction slightly more general

Aurimas Vinckevicius, 08/12/2014 17:24:
> Can you post a PNX record you're seeing for this?

https://gist.github.com/nemobis/d2763e0f43da3d50c609

> The test case here
> does not match what I see. (i.e. the item type and creator list should
> look different based on your changes)

I've not yet tested. If you tell me what's the output you think good for 
such a PNX, I can define the test case accordingly and make it pass in 
other commits to be added in this PR. Does this make sense to you?

Concretely, I'm not sure what you want to do with
<creatorcontrib>Coriolano, Giovanni Battista (1590-1649)</creatorcontrib>
if anything