Add return_void to Task

rt/include/typon/task.hpp

@@ -138,7 +138,14 @@ namespace typon
       _coroutine.promise()._continuation = std::noop_coroutine();
       _coroutine.resume();
     }
+
+    void return_void() noexcept = delete;
   };
+
+  template <>
+  void Task<void>::return_void() noexcept
+  {
+  }
   
 }