Dask-geomodeling

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- Never return Categorical dtypes in the field_operations.Classify and
ClassifyFromColumns. This leads to pandas incompatibilities with later
operations (round, subtract, where, mask).

- Never return Categorical dtypes from ParseTextColumn. (79)

- field_operations.Where and field_operations.Mask now also allow non-boolean
conditionals. This was already the case for Where on pandas == 0.19.*. (78)

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- Added Exp, Log and Log10 RasterBlocks.

- Added "std" and "var" statistics to TemporalAggregate.

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- Fixed point requests for RasterizeWKT.

- Allow empty coordinate list in Place.

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- Make transformation exceptions more comprehensible.

- Check for matching time resolutions in raster.Clip.

- Added 'product' to raster.reduction STATISTICS.

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- Fix point requests in raster.Smooth.

- GDAL 3 compatibility fixes.

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- Implemented `RasterTiler`.

- Let raster.Mask accomodate int values larger than uint8.