Finish alpha channel. Refactor names.

crates/api/src/prelude.rs

crates/api/src/render_object/mod.rs

crates/render/src/raqote/mod.rs

crates/render/src/web/mod.rs

crates/theme/src/dark.css

crates/widgets/src/check_box.rs

crates/widgets/src/items_widget.rs

crates/widgets/src/lib.rs

crates/widgets/src/list_view.rs

crates/widgets/src/scroll_indicator.rs

crates/widgets/src/stack.rs

crates/widgets/src/switch.rs

crates/widgets/src/text_box.rs

examples/canvas.rs

examples/grid.rs

examples/widgets.rs

src/prelude.rs