This requires moving remove_all_children() from ParentNode to
Node, which makes ParentNode.cpp empty, so remove it.
It also co-opts the existing Node::text_content() method and
tweaks it slightly to fit the semantics of Node.textContent.
This is a very barebones implementation of appendChild() that doesn't
take any of the idiosyncratic DOM behaviors into account yet.
Also teach the wrapper generator how to turn an Interpreter argument
into a Node&.
This patch introduces a hackish but functional IDL parser and uses it
to generate the JS bindings for Node and Document.
We'll see how far this simple parser takes us. The important thing
right now is generating code, not being a perfect IDL parser. :^)
