Dask-geomodeling

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- Accept categorical values in GeometryFileSink / to_file.

- Fixed incompatibilities with geopandas >=0.7.

- GeoJSON output is always converted to EPSG:4326 and doesn't have "crs" field.

- Implemented raster.reduction.reduce_rasters.

- Added the 'statistics' argument to raster.spatial.Place to deal with
overlapping features.

- Allow point requests in raster.spatial.Place.

- Clarifications about raster cell validity ranges in MemorySource and
RasterFileSource.

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- Accept list and dict values in GeometryFileSink / to_file.

- Fix bug in ParseTextColumn that added columns in duplicate when outputting
into the input column.

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- Fixed bug in `FillNoData` block.

- Fixed bug in `AggregateRasterAboveThreshold` (introduced in 37) (44).

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- Allow up to 1E-7 in the GeoTransform 'tilt' terms to account for possible
float32 imprecision.

- Handle Nones in geometry.field_operations.Classify and ClassifyFromColumns.

- Validate if labels are unique in geometry.field_operations.Classify and
ClassifyFromColumns.

- Added raster.spatial.Place.

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- Fix AggregateRaster: it now returns NaN for no data pixels (37)

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- Added GeometryWKTSource.

- Updated all docstrings.

- Renamed the 'location' parameter of raster.misc.Step to 'value'.