refactored window storage;

new helper window events (Destroyed, Created);
clippy + fmt;

core/src/window/settings/wasm.rs

@@ -0,0 +1,11 @@
+//! Platform specific settings for WebAssembly.
+
+/// The platform specific window settings of an application.
+#[derive(Debug, Clone, PartialEq, Eq, Default)]
+pub struct PlatformSpecific {
+    /// The identifier of a DOM element that will be replaced with the
+    /// application.
+    ///
+    /// If set to `None`, the application will be appended to the HTML body.
+    pub target: Option<String>,
+}