docs: fixed links in tokio-timer (#844)

* docs: fixed links in tokio-timer/src/timer/mod.rs

* docs: fixed links in tokio-timer::clock

tokio-timer/src/clock/clock.rs

@@ -10,8 +10,11 @@ use std::time::Instant;
 
 /// A handle to a source of time.
 ///
-/// `Clock` instances return `Instant` values corresponding to "now". The source
-/// of these values is configurable. The default source is `Instant::now()`.
+/// `Clock` instances return [`Instant`] values corresponding to "now". The source
+/// of these values is configurable. The default source is [`Instant::now`].
+/// 
+/// [`Instant`]: https://doc.rust-lang.org/std/time/struct.Instant.html
+/// [`Instant::now`]: https://doc.rust-lang.org/std/time/struct.Instant.html#method.now
 #[derive(Default, Clone)]
 pub struct Clock {
     now: Option<Arc<Now>>,
@@ -69,8 +72,10 @@ impl Clock {
         }
     }
 
-    /// Return a new `Clock` instance that uses `Instant::now()` as the source
+    /// Return a new `Clock` instance that uses [`Instant::now`] as the source
     /// of time.
+    /// 
+    /// [`Instant::now`]: https://doc.rust-lang.org/std/time/struct.Instant.html#method.now
     pub fn system() -> Clock {
         Clock {
             now: None,

tokio-timer/src/clock/mod.rs

@@ -4,15 +4,16 @@
 //! the source of time may be configured. This allows mocking out the source of
 //! time in tests.
 //!
-//! The [`now`][n] function returns the current `Instant`. By default, it delegates
-//! to [`Instant::now`][std].
+//! The [`now`][n] function returns the current [`Instant`]. By default, it delegates
+//! to [`Instant::now`].
 //!
 //! The source of time used by [`now`][n] can be configured by implementing the
 //! [`Now`] trait and passing an instance to [`with_default`].
 //!
 //! [n]: fn.now.html
 //! [`Now`]: trait.Now.html
-//! [std]: https://doc.rust-lang.org/std/time/struct.Instant.html
+//! [`Instant`]: https://doc.rust-lang.org/std/time/struct.Instant.html
+//! [`Instant::now`]: https://doc.rust-lang.org/std/time/struct.Instant.html#method.now
 //! [`with_default`]: fn.with_default.html
 
 mod clock;

tokio-timer/src/clock/now.rs

@@ -1,12 +1,14 @@
 use std::time::Instant;
 
-/// Returns `Instant` values representing the current instant in time.
+/// Returns [`Instant`] values representing the current instant in time.
 ///
 /// This allows customizing the source of time which is especially useful for
 /// testing.
 ///
 /// Implementations must ensure that calls to `now` return monotonically
-/// increasing `Instant` values.
+/// increasing [`Instant`] values.
+/// 
+/// [`Instant`]: https://doc.rust-lang.org/std/time/struct.Instant.html
 pub trait Now: Send + Sync + 'static {
     /// Returns an instant corresponding to "now".
     fn now(&self) -> Instant;