Export complex numbers to netcdf

[jenshnielsen]

• Basic test that complex numbers can be exported
• Fix the issue see http://xarray.pydata.org/en/stable/howdoi.html

[jenshnielsen]

One question remains. Should we completely drop the netcdf4 package and go with h5netcdf for all the export?

You can read about h5netcdf here https://pypi.org/project/h5netcdf/ and why the author anyway thinks its better than the netcdf4 python package

[astafan8]

Should we completely drop the netcdf4 package

i think we should. i really don't like myself this situation with hdf5 being behind a netcdf interface that does not have full feature parity thus producing invalid netcdf (but valid hdf5), but - if there's one storage format/engine, then it's easier to maintain, right? and we must let users export data with complex numbers, no way around that. so i'm happy to use h5netcdf only.

[codecov]

Codecov Report

Merging #3126 (65da543) into master (2a37d6e) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3126   +/-   ##
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  Coverage   65.66%   65.67%           
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  Files         216      216           
  Lines       28765    28769    +4     
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+ Hits        18889    18893    +4     
  Misses       9876     9876           

[jenshnielsen]

This ended up requiring to bump the minimum versions of xarray and in turn numpy and pandas