Pygeoprocessing

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* Versioning is now handled by ``setuptools_scm`` rather than
``natcap.versioner``. ``pygeoprocessing.__version__`` is now fetched from
the package metadata.
* Raster creation defaults now set "COMPRESS=LZW" for all rasters created in
PyGeoprocessing, including internal temporary rasters. This option was
chosen after profiling large raster creation runs on platter hard drives.
In many cases processing time was dominated by several orders of magnitude
as a write-to-disk. When compression is turned on overall runtime of very
large rasters is significantly reduced. Note this otherwise increases the
runtime small raster creation and processing by a small amount.
* ``pygeoprocessing.routing`` module now has a ``fill_pits``, function which
fills hydrological pits with a focus on runtime efficiency, memory space
efficiency, and cache locality.
* ``pygeoprocessing.routing`` module has a ``flow_dir_d8`` that uses largest
slope to determine the downhill flow direction.
* ``pygeoprocessing.routing`` module has a ``flow_accumulation_d8`` that uses
a pygeoprocessing D8 flow direction raster to calculate per-pixel flow
accumulation.
* Added a ``merge_rasters`` function to ``pygeoprocessing`` that will mosaic a
set of rasters in the same projection, pixel size, and band count.

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* Added an optional parameter to ``iterblocks`` to allow the ``largest_block``
to be set something other than the PyGeoprocessing default. This in turn
allows the ``largest_block`` parameter in ``raster_calculator`` to be passed
through to ``iterblocks``.
* Upgraded PyGeoprocessing GDAL dependency to >=2.0.
* Added a ``working_dir`` optional parameter to ``zonal_statistics``,
``distance_transform_edt``, and ``convolve_2d`` which specifies a directory
in which temporary files will be created during execution of the function.
If set to ``None`` files are created in the default system temporary
directory.

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* Fixed an issue where NETCDF files incorrectly raised Exceptions in
``raster_calculator`` and ``rasterize`` because they aren't filepaths.
* Added a NullHandler so that users wouldn't get an error that a logger
handler was undefined.
* Added ``ignore_nodata``, ``mask_nodata``, and ``normalize_kernel`` options
to ``convolve_2d`` which make this function capable of adapting the nodata
overlap with the kernel rather than zero out the result, as well as on
the fly normalization of the kernel for weighted averaging purposes. This
is in part to make this functionality more consistent with ArcGIS's
spatial filters.

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* When testing for raster alignment ``raster_calculator`` no longer checks the
string equality for projections or geotransforms. Instead it only checks
raster size equality. This fixes issues where users rasters DO align, but
have a slightly different text format of the WKT of projection. It also
abstracts the problem of georeferencing away from raster_calculator that is
only a grid based operation.

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* Changed the error message in ``reclassify_raster`` so it's more informative
about how many values are missing and the values in the input lookup table.
* Added an optional parameter ``target_nodata`` to ``convolve_2d`` to set the
desired target nodata value.

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* Hotfix to fix an issue with ``iterblocks`` that would return signed values
on unsigned raster types.
* Hotfix to correctly cite Natural Capital Project partners in license and
update the copyright year.
* Hotfix to patch an issue that gave incorrect results in many PyGeoprocessing
functions when a raster was passed with an NoData value. In these cases the
internal raster block masks would blindly pass through on the first row
since a test for ``numpy.ndarray == None`` is ``False`` and later
``x[False]`` is the equivalent of indexing the first row of the array.