Rename Sleep to Delay (#270)

This patch renames `Sleep` from tokio-timer and the tokio facade to
`Delay`. Given that the future does not actually put anything to sleep,
the `Delay` name feels more appropriate.

Fixes #263

tokio-timer/src/interval.rs

@@ -1,4 +1,4 @@
-use Sleep;
+use Delay;
 
 use futures::{Future, Stream, Poll};
 
@@ -8,7 +8,7 @@ use std::time::{Instant, Duration};
 #[derive(Debug)]
 pub struct Interval {
     /// Future that completes the next time the `Interval` yields a value.
-    sleep: Sleep,
+    delay: Delay,
 
     /// The duration between values yielded by `Interval`.
     duration: Duration,
@@ -26,12 +26,12 @@ impl Interval {
     pub fn new(at: Instant, duration: Duration) -> Interval {
         assert!(duration > Duration::new(0, 0), "`duration` must be non-zero.");
 
-        Interval::new_with_sleep(Sleep::new(at), duration)
+        Interval::new_with_delay(Delay::new(at), duration)
     }
 
-    pub(crate) fn new_with_sleep(sleep: Sleep, duration: Duration) -> Interval {
+    pub(crate) fn new_with_delay(delay: Delay, duration: Duration) -> Interval {
         Interval {
-            sleep,
+            delay,
             duration,
         }
     }
@@ -42,15 +42,15 @@ impl Stream for Interval {
     type Error = ::Error;
 
     fn poll(&mut self) -> Poll<Option<Self::Item>, Self::Error> {
-        // Wait for the sleep to be done
-        let _ = try_ready!(self.sleep.poll());
+        // Wait for the delay to be done
+        let _ = try_ready!(self.delay.poll());
 
-        // Get the `now` by looking at the `sleep` deadline
-        let now = self.sleep.deadline();
+        // Get the `now` by looking at the `delay` deadline
+        let now = self.delay.deadline();
 
         // The next interval value is `duration` after the one that just
         // yielded.
-        self.sleep.reset(now + self.duration);
+        self.delay.reset(now + self.duration);
 
         // Return the current instant
         Ok(Some(now).into())