Integrate timers with runtime. (#266)

This patch integrate the new timer implementation with the runtime by
initializing a timer per worker thread. This allows minimizing the
amount of synchronization needed for using timers.

src/util/mod.rs

@@ -0,0 +1,9 @@
+//! Utilities for working with Tokio.
+//!
+//! This module contains utilities that are useful for working with Tokio.
+//! Currently, this only includes [`FutureExt`][FutureExt]. However, this will
+//! include over time.
+
+mod future;
+
+pub use self::future::FutureExt;