Implement the "Advanced" feature set from Iced.

This commit intends to implement a majority of the functionality needed
when creating custom `iced` widgets.

src/advanced.rs

@@ -0,0 +1,19 @@
+//! Leverage advanced concepts like custom widgets.
+// pub use crate::application::Application;
+pub use iced_core::clipboard::{self, Clipboard};
+pub use iced_core::image;
+pub use iced_core::layout::{self, Layout};
+pub use iced_core::mouse;
+pub use iced_core::overlay::{self, Overlay};
+pub use iced_core::renderer::{self, Renderer};
+pub use iced_core::svg;
+pub use iced_core::text::{self, Text};
+pub use iced_core::widget::{self, Widget};
+pub use iced_core::Hasher;
+pub use iced_core::Shell;
+pub use iced_renderer::graphics;
+
+// pub mod subscription {
+//     //! Write your own subscriptions.
+//     pub use iced_runtime::futures::subscription::{EventStream, Hasher, Recipe};
+// }

src/lib.rs

@@ -58,6 +58,7 @@ use iced_widget::style::Theme;
 /// as much as possible.
 pub mod iced;
 
+pub mod advanced;
 mod conversions;
 mod render;
 mod systems;