timer: define sleep() as pub

src/timer.rs

@@ -41,7 +41,7 @@ pub fn now() -> u32 {
 }
 
 /// block for at least `amount` milliseconds
-fn sleep(amount: u32) {
+pub fn sleep(amount: u32) {
     use crate::timer::now;
     let start = now();
     while now() - start <= amount {}