index some new features from the main doxygen index

doc/main.txt

@@ -16,6 +16,10 @@
  *    - an os-independent interface to get write-only access to a file: ns3::SystemFile
  *    - an os-independent interface to get access to the elapsed wall clock time: ns3::SystemWallClockMs
  *    - a class to register regression tests with the test manager: ns3::Test and ns3::TestManager
+ *    - debugging facilities: \ref debugging, \ref assert, \ref error
+ *    - \ref randomvariable
+ *    - a class to handle automatic deletion of multiple sets of objects of different types: 
+ *      ns3::ObjectContainer
  *
  * The "simulator" module contains:
  *    - a time management class to hold a time and convert between various time units: ns3::Time