Mark io_service::work as deprecated.

asio/include/asio/io_service.hpp

diff --git a/asio/include/asio/io_service.hpp b/asio/include/asio/io_service.hpp
index 4657e04..1576983 100644
--- a/asio/include/asio/io_service.hpp
+++ b/asio/include/asio/io_service.hpp
@@ -616,7 +616,8 @@
 #endif // !defined(GENERATING_DOCUMENTATION)
 
 
-/// Class to inform the io_service when it has work to do.
+/// (Deprecated: Use executor_work.) Class to inform the io_service when it has
+/// work to do.
 /**
  * The work class is used to inform the io_service when work starts and
  * finishes. This ensures that the io_service object's run() function will not