v0.18.2

• Fix async_hn! handlers in the app scope unsubscribing after first event.
• Fix layout dependent on LayoutMetrics::screen_ppi not updating on change.
• Add Var::flat_map_vec for mapping Var<Vec<T>> to Var<Vec<O>> where T projects a Var<O>.
• Default setting editor reset button is now localizable in the zng-wgt-settings l10n resources.
  • Also surface it in zng::config::settings::editor::reset_button for use in custom editors.
• Implement FromStr for resolution units.
• Implement more Option conversions for response vars.
  • You can now map_into from ResponseVar<Option<T>> to Var<Option<T>>.
• Add flat_expr_var!, a helper for declaring an expression var that flattens.
• Fix EXIF metadata reading to define ppi.

Crates will be available on crates.io once Publish completes.