Make the tag type used by the await "keyword" part of the public interface.

asio/include/asio/coroutine.hpp

diff --git a/asio/include/asio/coroutine.hpp b/asio/include/asio/coroutine.hpp
index 005af2a..f1c4cba 100644
--- a/asio/include/asio/coroutine.hpp
+++ b/asio/include/asio/coroutine.hpp
@@ -319,9 +319,11 @@
   int value_;
 };
 
-namespace detail {
+/// Used to as a return value to tag functions that will generate an @c await
+/// result for a coroutine.
+template <typename T> class awaitable {};
 
-template <typename T> class coroutine_async_result {};
+namespace detail {
 
 class coroutine_ref
 {
@@ -357,14 +359,14 @@
 
   // Operator used to associate a variable to store the async result.
   template <typename T>
-  coroutine_async_result<T> operator&(T& t)
+  awaitable<T> operator&(T& t)
   {
     *async_result_ = &t;
-    return coroutine_async_result<T>();
+    return awaitable<T>();
   }
 
   // This overload is used when the result is ignored. 
-  template <typename T> void operator&(coroutine_async_result<T>)
+  template <typename T> void operator&(awaitable<T>)
   {
   }
 

asio/include/asio/impl/go.hpp

diff --git a/asio/include/asio/impl/go.hpp b/asio/include/asio/impl/go.hpp
index 1d6fa06..45ac9b9 100644
--- a/asio/include/asio/impl/go.hpp
+++ b/asio/include/asio/impl/go.hpp
@@ -336,7 +336,7 @@
 class async_result<detail::stackless_handler<Handler, T> >
 {
 public:
-  typedef detail::coroutine_async_result<T> type;
+  typedef awaitable<T> type;
 
   explicit async_result(detail::stackless_handler<Handler, T>&)
   {