Pyhomogenize

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* set proleptic_gregorian to standard calendar

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* convert time axis to CFTimeIndex

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* save_xrdataset is now working if Dataset does not include `time`

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* add `decode_times` and `combine` as keyword argumnets to `open_xrdataset`
* set default value of parallel in `open_xrdataset` to False

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* precise mid of time range
* add more dependencies (cftime, netcdf4, h5netcdf)

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* add data via pip install