Add node.innerHTML
Fix whitespaces

Initial Coding Style Guidelines created.
New code should try to conform to these standards
so that it is as easy to maintain as existing code.

Of course every rule has an exception,
but it's important to know the rules nonetheless!
Add document.createComment Conflicts: 	index.js
Fix createComment to follow spec
Refactoring

- Move helpers out from prototype
- Use getters for firstChild/lastChild/previousSibling/nextSibling
- Rename context reference
Flatten DocumentFragment when inserted to document
Use getters/setters for textContent
Add node.ownerDocument
Cleanup
Fix cloneNode to preserve ownerDocument