game_tree. Initial XML game tree parsing.

Add classes for each of the basic nodes in the tree.
Read the XML file.
Parse each of the basic XML nodes, and create a python objet for each.
game_tree. Rename render object to render geometry
game_tree. Add string representation to all tree nodes.
game_tree. Change root string reprentation to specify it's the root object.

Add object utility method to create string representation of object content.
game_tree. Add parsing of game information.

Add game, renderer and render pass node parsing.
Change parsing of other nodes to pass the game node for global testing of parsing.