Support for adding to specific elements

[refi64]

Right now, insertionQuery adds the style element directly to document.head, and the event listener is placed directly on the document. This is a problem, though, because it makes it impossible for a web component to use insertionQuery on its own shadow DOM!

A "fix" would be to allow a custom root element to be specified (since you can put style tags in the body) instead.

[naugtur]

great idea.

I'm not sure if I'll have the chance to get down to it soon, so feel free to try a pull request. I can help you out.

Conceptually, this would go in the function as an optional styleParent value that defaults to document.head

Let me know if you're interested.