- Migrating mrogers's changes to Renderable repo from Approach repo
 * Refactored XML class
  **Render pipeline is now Render-->RenderHead-->RenderCorpus-->RenderTail
  **Compatibility with C# XML class increased
 * Documentation comments

- Added abstract base class RenderNode<OutStream>
- Changed namespaces
- Moved << overloads into the XML class

Signed-off-by: Garet Claborn <garet@approachfoundation.org>