Add doxygen groups "Apparatuses" and "Decoders"
  Make sure every class is in a group
  Make sure most classes have a \brief description
  Improve comments for some classes including THcHallCSpectrometer
     and hodoscope classes
  Change some Doxyfile defaults.  Include sources files.

  in THcDummySpectrometer and THcTrigApp
  by removing calls to DefineVarsFromList that are not needed because
  those classes define no variables.

As it turns out, this was not so easy fix. I had to do:
- add at least c++0x support to scons (works for g++ 4.4.7!)
- change how my DefineVariables works

The c++0x support is bonus, since now we can use some additional features, like auto keyword (see https://gcc.gnu.org/gcc-4.4/cxx0x_status.html).