[Sphinx] Update the Tracing chapter in the Tutorial.

doc/tutorial/source/building-topologies.rst

@@ -1,6 +1,8 @@
 .. include:: replace.txt
 .. highlight:: cpp
 
+.. _BuildingTopologies:
+
 Building Topologies
 -------------------
 

doc/tutorial/source/data-collection.rst

@@ -178,6 +178,8 @@ by hooking the data collection components to |ns3| trace sources, and
 marshaling the data into a formatted ``gnuplot`` and into a formatted
 text file.  In the next sections, we'll review each of these.
 
+.. _GnuPlotHelper:
+
 GnuplotHelper
 *************
 

doc/tutorial/source/tweaking.rst

@@ -5,6 +5,8 @@
 Tweaking
 --------
 
+.. _UsingLogging:
+
 Using the Logging Module
 ************************
 
@@ -412,6 +414,8 @@ message,
 Using Command Line Arguments
 ****************************
 
+.. _Attribute:
+
 Overriding Default Attributes
 +++++++++++++++++++++++++++++
 Another way you can change how |ns3| scripts behave without editing
@@ -722,6 +726,8 @@ they will automatically be available for setting by your users through the
 command line system.  If you are a script author, you can add new variables to 
 your scripts and hook them into the command line system quite painlessly.
 
+.. _UsingTracingSystem:
+
 Using the Tracing System
 ************************