Fstd2nc

* Improvements to xarray interface to utilize the CF conventions
metadata (such as auxiliary coordinates).
* Add station, leadtime, and reftime as auxiliary coordinates in series
files.
* Use the date of validity by default. Old behaviour (date of origin)
can be restored by using --dateo or --forecast-axis options.
* Added 'leadtime' and 'reftime' auxiliary coordinates to encode the
forecast information.
* Progress bar is enabled by default. Can be turned off with
--no-progress option.
* Added CF metadata for various grid projections (rotated pole, polar
stereographic, lat-lon).
* Decode surface types (ice, land, sea, etc.).
* Decode depth coordinate for ocean model output.
* Fix decoding of masked data in raw binary (X32) format.

* Fixed unlimited dimension specification for PyDAP interface.
* Workaround for bug in numpy 1.14 when using masked structured arrays.
* Fix forecast times for series files.
* Don't discard LA/LO fields. They needed in some circumstances such
as trajectory files.

* Faster scanning of input file headers.
* New --progress option to show a progress bar for long conversions.
* More speed optimizations for RPN date and IP1 value conversions.
* Faster determination of dimensions from the record headers, using
pandas package.
* Restructured the package so each feature is in a separate Python
module, for easier development.
* Added xarray interface to facilitate custom netCDF conversions from
Python.

* Faster I/O when converting multiple input files.

* Support for ''scale_factor'' and ''offset'' attributes in metadata
files, as a rudimentary form of unit conversion.
* New --zlib option for compression of netCDF files.
* Some speed optimizations for converting to netCDF4:
- Chunk size is set equal to FSTD record size.
- FSTD records are read in order, to better utilize buffering /
read-ahead on the input file(s).

* ''station_id'' axis for series files.
* Allow --squash-forecasts to work on series data (only with one date
of origin).
* New --subgrid-axis option for splitting supergrids (e.g. yinyang)
into multiple sub-grids that are aligned on a ''subgrid'' axis.
* Experimental [https://github.com/pydap/pydap pydap] plugin for
browsing FSTD files through a web interface. To test it:
python -m pydap.wsgi.app
* Allow directory names and wildcard patterns (surrounded by quotes)
as inputs to the converter.
* Speed optimizations for RPN date and IP1 value conversions.
* Speed optimizations for data type detection (dtype_fst2numpy).
* Speed optimizations for --filter option
* Experimental (and undocumented) --quick-scan option to quickly
extract record headers from input files. Gives a good speed boost
when reading many input files, but relies on some internal structures
of librmn.
* New --msglvl option to control verbosity of librmn messages.
Default is changed to display only warning / error. Old behaviour
can be restored by using --msglvl=INFORM.