public boolean isDocument() determines if the node is a
      document.
    Parameters
None
Returns
Returns a boolean. True if the node is a document, false otherwise.
Example
    Node node = getTestNode(session, "ClimbingVolcanoes.JPG");
    
    Log.d(TAG, "isDocument: " + node.isDocument());      
      
      Would return output such as the following:
    isDocument: true