changed the way to access nodes and attributes from a node

changed the way to access nodes and attributes from a node

Before:
  Nodes were accessed via node properties ($node->body)
  Attributes were accessed via node array access ($node['name'])

After:
  Nodes are accessed via getNode(), setNode(), ... ($node->getNode('body'))
  Attributes are accessed via getAttribute(), setAttribute(), ... ($node->getAttribute('name'))

The change was necessary because of side-effects. This is one more time the
demonstration that being explicit is always better than magic ;)