timer: introduce delay function shortcut (#1440)

This commit adds a simple delay shortcut to avoid writing Delay::new
everywhere and removes usages of Delay::new.

tokio-timer/src/delay.rs

@@ -33,7 +33,7 @@ impl Delay {
     /// Only millisecond level resolution is guaranteed. There is no guarantee
     /// as to how the sub-millisecond portion of `deadline` will be handled.
     /// `Delay` should not be used for high-resolution timer use cases.
-    pub fn new(deadline: Instant) -> Delay {
+    pub(crate) fn new(deadline: Instant) -> Delay {
         let registration = Registration::new(deadline, Duration::from_millis(0));
 
         Delay { registration }

tokio-timer/src/lib.rs

@@ -59,9 +59,14 @@ pub use timer::{set_default, Timer};
 
 use std::time::{Duration, Instant};
 
+/// Create a Future that completes at `deadline`.
+pub fn delay(deadline: Instant) -> Delay {
+    Delay::new(deadline)
+}
+
 /// Create a Future that completes in `duration` from now.
 pub fn sleep(duration: Duration) -> Delay {
-    Delay::new(Instant::now() + duration)
+    delay(Instant::now() + duration)
 }
 
 // ===== Internal utils =====