Various Doxygen fixes.

montecarlo/doc/index.md

 \defgroup montecarlo The Monte Carlo related packages.
+\brief Monte Carlo packages
\ No newline at end of file

montecarlo/eg/doc/index.md

 \defgroup eg The particles related classes
 \ingroup montecarlo
+\brief Particle Data Group interface
 
-This directory contains classes with interfaces to the Particle Data Group (PDG)
+These classes are interfaces to the Particle Data Group (PDG)
 data base, a static and dynamic particle class and a decay class framework.
 
 These classes are extensively used in the VMC (Virtual Monte Carlo).

montecarlo/pythia6/doc/index.md

 \defgroup pythia6 The Pythia6 interface
 \ingroup montecarlo
-
-The pythia6 directory is an interface to the F77 version of Pythia 6.2 event generators, written by T.Sjostrand.
+\author T.Sjostrand
+\brief Pythia6 is an interface to the F77 version of Pythia 6.2 event generators
 
 See also the [complete Pythia6 documentation](http://home.thep.lu.se/~torbjorn/pythiaaux/recent.html)
 

montecarlo/pythia8/doc/index.md

 \defgroup pythia8 The Pythia8 interface
 \ingroup montecarlo
 \author T.Sjostrand.
-
-The pythia8 directory is an interface to the C++ version of Pythia 8.1 event generators.
+\brief The pythia8 directory is an interface to the C++ version of Pythia 8.1 event generators.
 
 The user is assumed to be familiar with the Pythia8 package.
 Only a basic interface to Pythia8 is provided. Because Pythia8 is

montecarlo/vmc/doc/index.md

-\defgroup vmc VirtuaL Monte Carlo
+\defgroup vmc Virtual Monte Carlo
 \ingroup montecarlo
+\brief Virtual interface to Monte Carlo packages
 
 More details can be found in [the Virtual Monte Carlo documentation](https://root.cern.ch/vmc).
 

tutorials/pythia/pythia8.C

@@ -8,16 +8,11 @@
 ///  root > .x pythia8.C
 /// ~~~
 ///
-/// \macro_image
-/// \macro_output
-///
 /// Note that before executing this script,
 ///
 ///  - the env variable PYTHIA8 must point to the pythia8100 (or newer) directory
 ///  - the env variable PYTHIA8DATA must be defined and it must point to $PYTHIA8/xmldoc
 ///
-/// \macro_code
-///
 /// \author Andreas Morsch
 
 void pythia8(Int_t nev  = 100, Int_t ndeb = 1)

tutorials/pythia/pythiaExample.C

 /// \file
 /// \ingroup tutorial_pythia
 /// Using Pythia6 with ROOT
+///
 /// To make an event sample (of size 100) do
 ///
 /// ~~~ {.cpp}