Add methods to set ControlFlow operation

This allows downstream users to avoid importing `ControlFlow` from winit.

examples/cursor.rs

@@ -1,7 +1,7 @@
 use simple_logger::SimpleLogger;
 use winit::{
     event::{ElementState, Event, KeyboardInput, WindowEvent},
-    event_loop::{ControlFlow, EventLoop},
+    event_loop::EventLoop,
     window::{CursorIcon, WindowBuilder},
 };
 
@@ -15,7 +15,7 @@ fn main() {
     let mut cursor_idx = 0;
 
     event_loop.run(move |event, _, control_flow| {
-        *control_flow = ControlFlow::Wait;
+        control_flow.set_wait();
 
         match event {
             Event::WindowEvent {
@@ -42,7 +42,7 @@ fn main() {
                 event: WindowEvent::CloseRequested,
                 ..
             } => {
-                *control_flow = ControlFlow::Exit;
+                control_flow.set_exit();
             }
             _ => (),
         }