Cfgrib

---------------------

- added --var-encoding-json (or -v) option to the to_netcdf tool, e.g.
``cfgrib to_netcdf -v '{"dtype": "float", "scale_factor": 0.1}' -o $OUTFILE $INFILE``
See `334 <https://github.com/ecmwf/cfgrib/pull/334>`_.
- fix issue where xarrays derived from Gaussian grids did not have the correct
geometry when written back out as GRIB
See `330 <https://github.com/ecmwf/cfgrib/issues/330>`_.
- fix issue where open_datasets() could merge different GRIB fields
that have the same data values
See `336 <https://github.com/ecmwf/cfgrib/issues/336>`_.

---------------------

- large reduction in memory leak
See `320 <https://github.com/ecmwf/cfgrib/pull/320/>`_.

- Replaced ``distutils.version`` by ``packaging.version`` and
added description and url to the xarray plugin.
See `318 <https://github.com/ecmwf/cfgrib/pull/318/>`_.

---------------------

- added --netcdf_kwargs_json option to 'cfgrib to_netcdf'
See `294 <https://github.com/ecmwf/cfgrib/pull/294/>`_.
- fixed support for GRIB files with alternativeRowScanning=1
See `296 <https://github.com/ecmwf/cfgrib/pull/296/>`_.
- fixed support for missing values
See `313 <https://github.com/ecmwf/cfgrib/issues/313>`_.

---------------------

- Fix failure to read index files.
See `292 <https://github.com/ecmwf/cfgrib/issues/292>`_.
- Allow backend kwargs to be provided in the to_netcdf executable,
either via a json format string, or a path to a json file via -b.
See `288 <https://github.com/ecmwf/cfgrib/pull/288/>`_.
- Fixed issue where the use of relpath() could cause a problem on Windows.
See `284 <https://github.com/ecmwf/cfgrib/issues/284>`_.
- Fix passing of pathlib.Path.
See `282 <https://github.com/ecmwf/cfgrib/issues/282>`_.
- Fixed issue where writing an ensemble number into a GRIB file caused an error.
See `278 <https://github.com/ecmwf/cfgrib/issues/278>`_.

---------------------

- Big internal refactor to add support for a generic ``Fieldset`` similar to Metview.
See `243 <https://github.com/ecmwf/cfgrib/issues/243>`_.

--------------------

- Fix the plugin interface that was missing ``extra_coords``.
See `231 <https://github.com/ecmwf/cfgrib/issues/231>`_.
- Fix the crash when ``extra_coords`` return a scalar.
See `238 <https://github.com/ecmwf/cfgrib/issues/238>`_.
- Improve type-hints.
Needed by `243 <https://github.com/ecmwf/cfgrib/issues/243>`_.