Fstd2nc

* Fixed a crash in recent versions of "progress" module when there are
no records to convert.
* Warn if no data was converted.
* Add an option to keep the 'LA' and 'LO' records instead of pruning
them as redundant information (e.g. if ^^ and >> are also available).
* For special case were ONLY lat/lon information is in the FST file,
produce a netCDF file with the lat/lon fields. These coordinates
were being stripped out (leaving an empty netCDF file) due to
aggressive pruning.

* New --compression parameter, to control the compression level for
netCDF4. Used in conjunction with --zlib parameter. Thanks to
David Landry for the patch.
* Fixed a crash when printing the progress bar in a locale that does
not support unicode.

* Loosen horizontal coordinate matching criteria for series data.
* Blacklist numpy 1.15.3, which had a bug that caused a fatal crash.

* Fixed the --ignore-typvar option, which was crashing.
* Fixed the encoding of depths shallower than 1m. These were
getting truncated to 0m.
* Fixed a bug in handling lists of values in attributes. This was
causing problems when using --rpnstd-metadata on files with a
"!!" vertical coordinate.
* Added two new command-line arguments --diag-as-model-level and
--ignore-diag-level, to deal with diagnostic-level data in the
FSTD file.
* Detect mixture of diagnostic / model levels and inform the user
of how to resolve this using the above commands.
* Package should now be fully compatible with Python 3.
* Added docstring to the fstd2nc.Buffer class.

* Fixed .to_pygeode() method, which was failing on xarray > 0.10.0.
* Added locks to thread-unsafe parts of the code.
* Fixed a float64 upcasting that was done on some record parameters
when using pandas routines.
* Handle whitespace in list-based command-line arguments, e.g.
--vars="VAR1, VAR2, VAR3".
* Fixed a crash when using --rpnstd-metadata on vertical levels.

* Added 'station' as a coordinate for 'Y' series data.
* Some incremental speedups in constructing Buffer objects.
* Command-line option to rename variables.
* Command-line option to create an 'ensemble' axis over varying
etikets.
* Some new features / improvements geared towards using this package
in Python scripts:
* Read FST records in their natural order in the xarray interface.
* Added an optional 'header_dict' parameter to Buffer, to allow it to
remember the headers of files that have been previously scanned.
* Added a to_iris() method to generate an Iris CubeList object.
* Added a to_pygeode() method to generate a PyGeode Dataset object.