[libsigcplusplus/libsigc++-2-10] signal: Document older syntax as deprecated.

[Murray Cumming <murrayc src gnome org>]

commit 2afeab2c25b5224beb65fb84b519414971a6c9e6
Author: Murray Cumming <murrayc murrayc com>
Date:   Sat Mar 12 17:40:47 2016 +0100

    signal: Document older syntax as deprecated.

 sigc++/macros/signal.h.m4 |   10 ++++++++++
 1 files changed, 10 insertions(+), 0 deletions(-)
---
diff --git a/sigc++/macros/signal.h.m4 b/sigc++/macros/signal.h.m4
index bc76c0d..99f66f0 100644
--- a/sigc++/macros/signal.h.m4
+++ b/sigc++/macros/signal.h.m4
@@ -453,6 +453,11 @@ FOR(1,$1,[
  * sig.emit(19);
  * @endcode
  *
+ * @deprecated Please use the syntax similar to that used by std::function<>:
+ * @code
+ * sigc::slot<void(bool, int)> some_slot;
+ * @endcode
+ *
  * @ingroup signal
  */
 template <LIST(class T_return, LOOP(class T_arg%1 = nil, $1))>
@@ -462,6 +467,11 @@ class signal],[dnl
  * See the base class for useful methods.
  * This is the template specialization of the unnumbered sigc::signal
  * template for $1 argument(s).
+ *
+ * @deprecated Please use the syntax similar to that used by std::function<>:
+ * @code
+ * sigc::slot<void(bool, int)> some_slot;
+ * @endcode
 ifelse($1, $2,[dnl
  *
  * @ingroup signal