v0.16.0: Release 0.16.0: icons from Lucide, Tabler and Simple Icons.

Icons from Lucide, Tabler and Simple Icons, behind the icons feature.

Added

• icon!("lucide:server") adds an icon by set and name: lucide:,
  tabler: (with -filled variants) and simple: for brand logos. Only
  the icons a project names are put into its binary. A name that does not
  exist fails to compile and lists the closest names.
• .size(), .color() and .stroke_width() on the builder; the Icon
  handle has color() and stroke_width() as signals, Icon::paths for
  draw_on, and Icon::style (IconStyle::Stroke or IconStyle::Fill).
  The color defaults to the theme's text color.
• Icon::from_svg makes the same node from a 24 by 24 SVG of your own.
• FlowDiagram puts an icon at the start of a card with
  .icon(name, icon!(..)); flow.icon(name) returns its handle.
• The architecture example.

Fixed

• Creating GPU renderers on several threads at once could crash inside the
  Vulkan driver. Renderers now share one Vulkan, Metal or DX12 instance;
  a GL-only machine still gets one per renderer.