refactored window storage;

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

core/src/window/position.rs

@@ -0,0 +1,22 @@
+/// The position of a window in a given screen.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Position {
+    /// The platform-specific default position for a new window.
+    Default,
+    /// The window is completely centered on the screen.
+    Centered,
+    /// The window is positioned with specific coordinates: `(X, Y)`.
+    ///
+    /// When the decorations of the window are enabled, Windows 10 will add some
+    /// invisible padding to the window. This padding gets included in the
+    /// position. So if you have decorations enabled and want the window to be
+    /// at (0, 0) you would have to set the position to
+    /// `(PADDING_X, PADDING_Y)`.
+    Specific(i32, i32),
+}
+
+impl Default for Position {
+    fn default() -> Self {
+        Self::Default
+    }
+}