Re-organize custom module as pipeline module

... and move `Shader` widget to `iced_widget` crate

examples/custom_shader/src/main.rs

@@ -3,15 +3,20 @@ mod cubes;
 mod pipeline;
 mod primitive;
 
+use crate::camera::Camera;
 use crate::cubes::Cubes;
+use crate::pipeline::Pipeline;
+
+use iced::executor;
+use iced::time::Instant;
 use iced::widget::{
     checkbox, column, container, row, slider, text, vertical_space, Shader,
 };
+use iced::window;
 use iced::{
-    executor, window, Alignment, Application, Color, Command, Element, Length,
-    Renderer, Subscription, Theme,
+    Alignment, Application, Color, Command, Element, Length, Renderer,
+    Subscription, Theme,
 };
-use std::time::Instant;
 
 fn main() -> iced::Result {
     IcedCubes::run(iced::Settings::default())

examples/custom_shader/src/primitive.rs

@@ -4,17 +4,18 @@ pub mod vertex;
 mod buffer;
 mod uniforms;
 
-use crate::camera::Camera;
-use crate::pipeline::Pipeline;
-use crate::primitive::cube::Cube;
+pub use buffer::Buffer;
+pub use cube::Cube;
+pub use uniforms::Uniforms;
+pub use vertex::Vertex;
+
+use crate::Camera;
+use crate::Pipeline;
+
 use iced::advanced::graphics::Transformation;
 use iced::widget::shader;
 use iced::{Color, Rectangle, Size};
 
-pub use crate::primitive::vertex::Vertex;
-pub use buffer::Buffer;
-pub use uniforms::Uniforms;
-
 /// A collection of `Cube`s that can be rendered.
 #[derive(Debug)]
 pub struct Primitive {