Implement Quicksilver score-based text matching for the jQuery version

Hope you'll consider this contribution for better search matching. I'll be using this in my project, as your search was not very good for my use case.

This uses Quicksilver-style score-based matching of all letters in the search text to the target text.

I've only added this to the jQuery version, but I expect you can fairly easily implement it in the prototype version as well.