Made api more Ruby-like and fixed some bugs.

These are some changes that I made a while back. I thought the api was maintained by shopstyle, so I submitted the PR to the wrong fork. Here it is again.
@rudolph9 as this is an age-old PR, and @troelskn don't even use ShopSense anymore, I guess this is up to you and I.

Are you alone in this, or do you receive support from the ShopSense team?