Dask-geomodeling

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- utils.get_crs now leaves EPSG codes instead of converting them to their Proj4
representation.

- Implemented GeometryFileSink that writes ESRI Shapefile, GeoJSON, GML, and
geopackage.

- Added a .to_file() method to all GeometryBlocks.

- Added dry_run parameter (for validation) to .to_file().

- Start using google docstring convention.

- Several minor doc fixes.

- Fix setting of the .crs property in the GeometryFileSource.

- Fixed serialization of raster.Classify.

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- Fix empty response of TemporalAggregate and Cumulative.

- Fix elementwise raster blocks in case of empty datasets.

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- Added RasterFileSource.close_dataset to close the GDAL file handle.

- Run unittests on windows.

- Adapt safe_abspath and safe_file_url functions: they now automatically
interpret the geomodeling.root config instead of the 'start' kwarg.

- Added a geomodeling.strict-file-paths that defaults to False. This changes
the default behaviour of all blocks that handle file paths: by default, the
path is not required to be in geomodeling.root.

- Added installation instructions for windows.

- Improved the ipyleaflet plugin so that it can deal with multiple notebook
servers on the same machine. The parameter 'hostname' was replaced by 'url'.

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- Fixed propagation of the 'extent' and 'geometry' attributes through the
raster.Clip. Both now return the intersection of the store and mask rasters.

- The MemorySource and elementwise blocks now return None for 'extent' and
'geometry' if they are empty.

- Preserve functionality of the geometry.Difference block with geopandas 0.6.
When taking the difference of a geometry with a missing geometry (A - None),
geopandas < 0.6 returned A as result, while >= 0.6 returns None as result.

- Added default values for RasterFileSource's time parameters.

- Implemented the 'columns' attribute for GeometryFileSource.

- Fixed the projection attribute of elementwise raster blocks in case one of
the arguments is a number and not a Block instance.

- Implemented the geo_transform attribute of elementwise raster blocks.

- Added an ipyleaflet plugin for visualizing RasterBlocks in jupyter notebook.

- Changed the default geomodeling.root setting to the current working directory

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- Added documentation.

- Fixed MemorySource incase of a request outside of the data boundary.

- Fixed multiple bugs in Reclassify and added some tests. The 'from' dtype can
now be boolean or integer, and the 'to' dtype integer or float. The returned
dtype is now decided by numpy (int64 or float64).

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- Clean up the .check() method for RasterBlocks.

- Added a Travisfile testing with against versions since 2017 on Linux and OSX.

- Took some python 3.5 compatibility measures.

- Added fix in ParseText block for pandas 0.23.

- Changed underscores in config to dashes for dask 0.18 compatibility.

- Constrained dask to >= 0.18, numpy to >= 1.12, pandas to >= 0.19,
geopandas to >= 0.4, scipy to >= 0.19.

- Removed the explicit (py)gdal dependency.