- introduce RenderableItem to support both owned and borrowed children in composite Renderables - refactor some of our gnarlier manual layouts, BottomPane and ChatWidget, to use ColumnRenderable - Renderable and friends now handle cursor_pos()
- introduce RenderableItem to support both owned and borrowed children in composite Renderables - refactor some of our gnarlier manual layouts, BottomPane and ChatWidget, to use ColumnRenderable - Renderable and friends now handle cursor_pos()