get product specifications

Hello,
I've added a method to get the "especification_list" from vtex. Not sure if I missed anything, could you please check when you have the time?

I've also pointed some fields that might be populated by vtex in order to avoid some discrepancies.

* and a small fix: replaces => with : for image urls. (probably a misreplace)
think you're right here, it's probably safe to remove this key from the request