Implement 'scons cppcheck=1' functionality ... plus a few other minor updates

Generate cppcheck_report.txt in the top level directory.

Also added versioned Hall C library to .gitignore

  Remove link to engine
  Remove quick.csh script
  Undo changes to hodtest.C and hodtest_cuts.def

just for test purpose.

These were related to a) scope of some variable declarations, and b) use
of pre-increment vs. post-increment of non-primitive types (this has a
slight performance hit due to the way that pre- vs. post-increment
operators are overloaded in C++.

Also cleaned up a few places where initialized variables were not being
used.

Modified THcAerogel::ReadDatabase

1) Need to add fNelem to DBRequest to read parameter arrays.
2) Added optional variable and set to true. Flag in the
DBRequest to tell code that parameter is optional
and does not have to be found.
3) Move setting of fNelem to before DBRequest for aero_num_pairs
 so that it can be overwritten by parameter file.

Update SCons compilation instructions in README.md, and improve 'scons -c' procedure.

purposes.

- Add MacOSX-dependent compile options in Hall C LinkDef

  Clone some DC tests from ENGINE test files to podd
  style cuts.  Make changes to source code to support these tests.
  Correct hits in plane line in example report file.

Add fThetaCentralOffset, fOopCentralOffset, fPCentralOffset

Report stuff

Add fTheta_lab
Do offsets in THcHallCSpectrometer::ReadDatabase

  If ThcAnalyzer::PrintReport sees a format descriptor with 'd' at
  the end, then the value is converted to the nearest int before formatting.

    Added variables using ENGINE names
       gen_run_number
       gen_run_starting_event
       gen_event_id_number

Add missing [fNelem] to comment for fA_Neg and fA_Neg_p declarations.

   This is magic that allows the size of arrays to passed to
   the root tree making.

Add template driven end of run reports to analyzer class

Inspired by ENGINE/CTP report generator
  Reports generated by
    THcAnalyzer::PrintReport(templatefilename,outputfilename)
    template is copied to output, {stuff} is replaced by the
       value of stuff.  Value can be formated with c formater, eg.
           {stuff:%.2f}
  ThcFormula added to allow more flexibility of variables.
    Can get number of times cuts pass or are called with:
       cutname.npassed (or cutname.scaler) and cutname.ncalled

Re-arrange, modify and make more detailed comments in the Shower*.h header
files. Add more comments in the Shower*.cxx files.

Changed column and row numbering in THcShowerHit.h in order to get rid of
warning messages on unsigned and integer comaprisons when compiling;

Corrected a debug message in THcShower.cxx.

Latest additions to Shower code