WIP. Code & doc cleanup. Moved doc for widgets to widget.rst.  Added default get method to DPage and modified pages to implement generate method.  Deleted DPage.render since no longer needed. Removed DWidget since widgets are now methods. Removed _render & _renderstr since no longer needed. Commented out widgets that still need conversion. Converted Row & RowColumn to new widget signature. Deleted RowColumnMap since no longer needed. Added tuple support to Text & StringDup.