[libsigcplusplus] docs: Slots: Add section titles to break it up.

[Murray Cumming <murrayc src gnome org>]

commit fbbe7c144f964e75afa6d257dac1ffeab9996c58
Author: Murray Cumming <murrayc murrayc com>
Date:   Fri Apr 1 11:08:45 2016 +0200

    docs: Slots: Add section titles to break it up.

 sigc++/functors/slot_base.h |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletions(-)
---
diff --git a/sigc++/functors/slot_base.h b/sigc++/functors/slot_base.h
index 2e27f76..affbc9d 100644
--- a/sigc++/functors/slot_base.h
+++ b/sigc++/functors/slot_base.h
@@ -199,7 +199,9 @@ struct SIGC_API slot_do_unbind
  * A slot can be constructed from any function object or function, regardless of
  * whether it is a global function, a member method, static, or virtual.
  *
- * Use the sigc::mem_fun() and sigc::ptr_fun() template functions to get a sigc::slot, like so:
+ * @section slots-creating Creating Slots
+ *
+ * Use the sigc::mem_fun() or sigc::ptr_fun() template functions to get a sigc::slot, like so:
  * @code
  * sigc::slot<void(int)> sl = sigc::mem_fun(someobj, &SomeClass::somemethod);
  * @endcode
@@ -216,6 +218,8 @@ struct SIGC_API slot_do_unbind
  *
  * You can also pass slots as method parameters where you might normally pass a function pointer.
  *
+ * @section slots-auto auto
+ *
  * sigc::mem_fun() and sigc::ptr_fun() return functors, but those functors are
  * not slots.
  * @code
@@ -226,6 +230,8 @@ struct SIGC_API slot_do_unbind
  * auto sl = sigc::mem_fun(someobj, &SomeClass::somemethod); // Not a slot!
  * @endcode
  *
+ * @section slots-with-lambdas C++ Lambdas
+ *
  * A C++11 lambda expression is a functor (function object). It is automatically
  * wrapped in a slot, if it is connected to a signal.
  * @code