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.

  THcRawHodoHit gives reference time corrected TDC values
  THcScintillator plane adds a per plane offset to the raw tdc value
  First positive TDC value after adding offset is used

   Don't repeat comparisons of tdc values
   with fScinTdcMin and fScinTdcMax because hits only get added to
   fHodoHits (and previously fPosTDCHits, fNegTDCHits, ...) if
   the times are within these ranges.
  In THcHodoscop, remove members of fTOFPInfo that are just used
   locally.