Add MouseEntered/MouseLeft for Windows, X11, Wayland, & Cocoa

src/events.rs

@@ -30,6 +30,12 @@ pub enum Event {
     /// The parameter are the (x,y) coords in pixels relative to the top-left corner of the window.
     MouseMoved(i32, i32),
 
+    /// The cursor has entered the window.
+    MouseEntered,
+
+    /// The cursor has left the window.
+    MouseLeft,
+
     /// A mouse wheel movement or touchpad scroll occurred.
     MouseWheel(MouseScrollDelta, TouchPhase),