[dom] Rename Elements to ElementList (#50)

"Elements" is super hard to search for (ex. web search don't find this), and is not clear what it does. It should also be constructible and writing new Elements([...]) is weird, new ElementList([....]) makes sense.

https://dom.spec.whatwg.org/#element-collections

---
Reply to this email directly or view it on GitHub:
https://github.com/whatwg/dom/issues/50