Add waker and conversion to raw pointer (#16)

diff --git a/src/raw.rs b/src/raw.rs
index 6af184f..c783d26 100644
--- a/src/raw.rs
+++ b/src/raw.rs
@@ -35,6 +35,9 @@
 
     /// Runs the task.
     pub(crate) run: unsafe fn(*const ()),
+
+    /// Creates a new waker associated with the task.
+    pub(crate) clone_waker: unsafe fn(ptr: *const ()) -> RawWaker,
 }
 
 /// Memory layout of a task.
@@ -131,6 +134,7 @@
                     drop_task: Self::drop_task,
                     destroy: Self::destroy,
                     run: Self::run,
+                    clone_waker: Self::clone_waker,
                 },
             });