added a way to get the whole set's price at once

Hi bedoherty, 
I forked your repository and have added a function that retrieves the whole set's price at once. I'm currently working on a android app, and found that getting each's card price one by one proved to be slower than it would be if I had the whole sets priced and then linked them up that way. I also edited your single card price to code that should work, but I haven't tested it because my computer is blocked from tcg or something... ( they have the db/magic_single_search redirecting to their shop page... so the code is meant to parse that... also grabbed the foil price.) I got to test it once before they blocked it, and I think it probably doesn't work because it's grabbing html before it redirects.... anyway, I hope you can use this. (also, I've uploaded a version of it to my own googleappsengine site so that i wasn't causing your server any problems.)