made painter actually how I wanted it (draw now takes in an owned painter)

src/core/stack.rs

@@ -1,11 +1,11 @@
-use crate::{Widget, WidgetId};
+use crate::{Painter, Widget, WidgetId};
 
 pub struct Stack {
     pub children: Vec<WidgetId>,
 }
 
 impl<Ctx> Widget<Ctx> for Stack {
-    fn draw(&self, painter: &mut crate::Painter<Ctx>) {
+    fn draw(&self, mut painter: Painter<Ctx>) {
         for child in &self.children {
             painter.draw(child);
         }