Ascat

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- Update file handling read_period
- Refactor xarray readers/writers into SwathFileCollection, CellFileCollection,
and CellFileCollectionStack
- Add tutorial for xarray readers/writers
- Add CLI for aggregating ASCAT swath data
- Add CLI for regridding ASCAT swath data to a regular lat/lon grid

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- Add str to path conversion for H SAF FTP download

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- Update interface of file handling module

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- Update to pyscaffold v4.5
- Update download module, supporting parallel download for EUMETSAT Data Store
- Update interface of file handling module

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- Add draft for indexed ragged array netcdf file reader using xarray
- Add ASCAT netcdf swath file reader

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- Add support reading ascat fmv 13 for szf, szr, szo