GRIB file version 1 generation library

This is a C++ library to generate GRIB version 1 files. It is based on Wesley
Ebisuzaki code for wgrib/gribw wrapped into some convenient objects.

Relevant objects are

#) GRIB_FILE
   Interface for accessing in Read or Write (+append) a GRIB file on disk. 

#) GRIB MESSAGE
   To access or compose and encode a grib message.

#) GRIB_FIELD
   The phisical parameter stored in the message

#) GRIB_GRID
   The grid definition

#) GRIB_LEVEL
   The level of the grid

#) GRIB_TIME
   The time of the grid

Every object srore as public data all informations.

Example to read a GRIB file from disk and dump contents:

[...]

  GRIB_FILE gf;

  int ret = gf.OpenRead("grib.grb");
  if (ret != 0) return -1;

  GRIB_MESSAGE m;

  while ((ret = gf.ReadMessage(m)) == 0)
  {
    std::cout << "Message:  " << m.field.VarDescription( ) << std::endl;
    std::cout << "Grid :    " << m.grid << std::endl
              << "Level:    " << m.level << std::endl
              << "Time :    " << m.gtime << std::endl << std::endl;

    // data field is at m.field.vals
    for (int i = 0; i < field.size; i ++)
      std::cout << "Value [" << i << "] :" << m.field.vals[i] << std::endl;

  }

  ret = gf.Close( );
  if (ret != 0) return -1;

[...]

Example to write a field to disk:

[...]

  GRIB_FILE gn;
  GRIB_MESSAGE m;
  GRIB_GRID g;
  GRIB_LEVEL l;
  GRIB_TIME t;
  GRIB_FIELD f;

  ret = gn.OpenWrite("outtest.grb");
  if (ret != 0) return -1;

  float ff[65160];

  // Read temperature values
  [...]

  [...]

  // set time: 12 hour forecast from 2004-07-03 12:00:00 UTC

  t.set_referencetime(2004, 7, 3, 12, 0);
  t.set_forecast_hour(12);

  // set level pressure at 1000 mb
  l.set_pressure(1000.0);

  // set grid
  g.set_size(360, 181);
  g.set_regular_latlon(90.0, 0.0, -90.0, -1.0, 1.0, 1.0);

  // set field values of temperature
  f.set_field(GRIB_PARAMETER_TMP__, ff, 65160, 9.9991e20, 9.9991e20);
  f.set_scale(-2);

  m.set_time(t);
  m.set_grid(g);
  m.set_level(l);
  m.set_field(f);

  // Encode message
  m.Encode( );

  // Write message
  gn.WriteMessage(m);

  // Repeat for all times and levels
  [...]

  [...]

  ret = gn.Close( );
  if (ret != 0) return -1;

[...]