Fstd2nc

* Detect when multiple '!!' records have identical coordinate systems.
Allow unstrict matching to one of these records if there are no exact
ig1/ig2/ig3 matches available.
* Fix filesize for netCDF4 header when using compatibility mode.

* Added "101010101" to list of known dummy dates, to avoid a crash in
HRDLPS file conversion.
* Added "TRAF" to the list of known surface fields, so it gets
annotated with the appropriate surface types.
* Renamed "sea_ice" to "lake_ice_or_sea_ice" in the list of surface
types, which is a more accurate description for the model data.
* Removed the "units" attribute for unitless level types. This was
originally added for COARDS compatibility, but is causing issues with
some netCDF utilities like Iris.
* When using --vardict or --opdict, put the definition string in an
attribute named "definition_opdict" instead of "description".
Suggested by Daniel Deacu.
* Fix a bug in metadata files which give units of "1" - it was getting
encoded as a numeral 1 instead of a string, causing grief with some
netCDF tools.

* Fix a bug when a fill value was trying to be applied to integer data.
* Fix a bug with negative integer values in netCDF3 encoding.
* Add support for "META" record from GenPhysX, which now gets converted
to a string type.
* New --opdict option to extract useful metadata from the operational
dictionary (on systems where $AFSISIO is available).
* New --vardict option for providing a custom CMC-RPN variable
dictionary (in their XML format) to extract metadata from.
* Can now override the "Conventions" attribute by passing in a value
with the new --conventions option.
* Can now easily disable "Conventions" attribute entirely by using the
new --no-conventions option.
* The keys in the metadata file passed in by --metadata-file are now
case sensitive, so can define attributes that use upper-case letters.
* Preliminary support for "underwater" levels defined by level type 7.
* New --thermodynamic-levels option to select only data on the
thermodynamic levels of a staggered vertical coordinate.
* New --no-adjust-rlon option for rotated grids, which disables the
value shift that's usually done to the rlon coordinate when it passes
over the dateline. Instead, the original (unshifted) coordinate is
used.
* Experimental new --fstd-compat option which allows the output file to
be used as both a netCDF and FSTD file (for compatibility with both
sets of tools).

* Fix a caching bug in dask wrapper. The cache was being shared among
all Buffer objects, so the wrong record may be returned under some
circumstances.

* Tweak the handling of metadata records to avoid erroneously treating
data records as metadata (such as when "SV" is actually a 2D field).
* Fix stack space for threads (default too small on science network).
Affects the xarray interface, not the command-line invocation.
* Metadata files now work better when using --rename argument. Both
the old and new names are valid section headers for the metadata.
* Treat diagnostic-level height (e.g. 1.5m) as a bottom model level
when it appears in conjunction with 3D model levels. The default
was to split it into a separate variable. The old behaviour can be
restored by using new argument --split-diag-level.

* 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.