h4h5tools

Implement _FillValue correctly.

- Always generate _FillValue attribute
   EOS2 handling routine stores _FillValue attribute if h4toh5 general routine cannot do this.
   - If an EOS2 field is stored as an HDF4 vdata (one-dimensional)
       _FillValue is always written in EOS2 handling routine
       H5Pset_fill_value() is called inside of EOS2 handling routine
   - If an EOS2 field is stored as an HDF4 sds (multi-dimensional)
       H5Pset_fill_value() is called by the general routine. (This changelist will perform this.)
       if the SDS has _FillValue attribute
          The general routine will convert it.
       else
          EOS2 handling routine will convert it.

- Test cases
   HDF-EOS2 has ten primitive types. Generates thorough test cases for each type. For each type,
   test cases of both EOS2 field and EOS2 attribute are generated.

- Bug fix regarding fill value
   The original h4toh5 routine has problem in converting fill value; it keeps this information
   only when the SDS is empty. Also, endianness was not correct.
   This changelist fixes these two problems.

All grid test cases were verified with verification tool, and I could check that the fill values read by HDF-EOS2 API were same as those ready by NetCDF4 API. All test cases were successfully dumped by ncdump.