feat: add complete DOM implementation with Document, Element, and NodeList classes to html module

test/html/nodelist_item.wren

@@ -0,0 +1,19 @@
+// retoor <retoor@molodetz.nl>
+
+import "html" for Document
+
+var doc = Document.parse("<div><p>A</p><p>B</p><p>C</p></div>")
+
+var list = doc.querySelectorAll("p")
+
+System.print(list.item(0).textContent) // expect: A
+System.print(list.item(1).textContent) // expect: B
+System.print(list.item(2).textContent) // expect: C
+
+System.print(list.item(0).tagName) // expect: P
+System.print(list.item(1).tagName) // expect: P
+System.print(list.item(2).tagName) // expect: P
+
+var single = doc.querySelectorAll("div")
+System.print(single.item(0).tagName) // expect: DIV
+