Shape refactor (#705)

* More introspection stats about vertices/indices etc

* more serde derive

* #[inline] to Shape constructors

* Introduce RectShape

* Introduce CircleShape

* Introduce PathShape

* More serde derive

* impl Copy for RectShape and CircleShape

* Simplify some code

* More serde derive

* Add helpers for appending more input or output

* Serde derives for RawInput

* Rename Fonts::from_definitions to Fonts::new

* Add Output::take

* refactor EguiGlium slightly

* Derive PartialEq for RawInput

* Improve egui::util::History interface

* tweaks

* Improve History filter: add minimum length

* Calculate galley bounding rect

* tessellator: cull line segments and paths

* tessellator: cull meshes

* Fix bug in History bandwidth estimator

epaint/src/stroke.rs

@@ -26,6 +26,12 @@ impl Stroke {
             color: color.into(),
         }
     }
+
+    /// True if width is zero or color is transparent
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.width <= 0.0 || self.color == Color32::TRANSPARENT
+    }
 }
 
 impl<Color> From<(f32, Color)> for Stroke