Remove patternID

I don't think that there's a use-case for the `patternID` property, since you can easily [use the polyfill on multiple unique elements that share a class](http://codepen.io/ChristianBundy/pen/Kstnm) by using the polyfill method only on the element that you want the polyfill active on.

I think that the `patternID` was a great idea for making sure that the polyfill is only active when it's supposed to be, but the method's use of `this` already confines it to the element that it's acting on, so it's safe to remove. This is also backward compatible, so long as the old version doesn't run the method on elements that aren't supposed to be polyfilled (which isn't the intended use for this anyway).