Remove Dependency on jQuery

jQuery's nice and all, but it's a bit of overkill for this script. So, I got rid of it and replaced things with native functions. I assure you, they're not as scary as they seem!

Also, `DOMSubtreeModified` is *super* noisy and will have a rather negative effect on this script's speed (especially when combined with a non-native query like a not-attribute selector). I switched it out to `MutationObserver`, which is way less hyperactive, but still gives you all of the benefits of `DOMSubtreeModified`.