New netcdf postprocessor

[jhardenberg]

The new tool scripts/srv2nc is a complete alternative to the afterburner, based on CDO.
It converts the full raw PlaSIM output files to (zipped) netcdf4. Already by doing so space requirement is halved. No information is lost and the original raw files could be erased after conversion. The suggestion is to use this directly in the run script to convert output on the fly. CDO can then be used for later postprocessing.

Additional features:

• correct Gaussian and Spectral grids are written
• a correct vertical hybrid-coordinate grid is written (for 3D outputs)
• a parameter table is implemented, which follows the afterburner docs conventions for variable names and units (a conversion to standard CMOR names will be implemented separately). This way netcdf variables get PlaSIM names and units.

From all tests, results are identical to afterburner output.
The tool works both with the main PlaSIM output (in that case it fixes the vertical coordinate axis and uses afterburner name conventions) and with the ML ocean and ice model output (in those cases it uses variable names and units as in the PlaSIM source code). An adaptation to convert also LSG files is being developed.

Usage: srv2nc [-d code1,code2,...] [-m] [-y] infile.nc outfile.nc
Options:
  -d codelist   remove a comma-separated list of codes from the output
  -m            perform monthly means
  -y            perform yearly means

[jhardenberg]

Due to the way that github works, this PR also contains other small changes, sorry about that. Just pick srv2nc if you do not care for those .....

[jhardenberg]

The tool now works also for LSG output and writes netcdf files with correct horizontal and vertical grids.