Node: Build an hierarchic tree of node elements

This class can be used to build an hierarchic tree of node elements.

Each node has a name. One or more children nodes can be added to a node object.

The class may also export the hierarchy of nodes to a XML document. It may also import a XML document and build an hierarchy of node objects from the XML tag nodes.

The children of a node may be accessed as object variables with the same names of the children nodes. Children with the same name can be accessed as arrays with a numeric index to distinguish each child node.