Pyflwdir

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New
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* Flwdir.river_depth for gradually varying flow (gvf) and manning river depth estimation
* Flwdir.path method to get the indices of flow paths for vector flow directions

Improved
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* FlwdirRaster.streams method includes a (zero-length) line at pits and adds option for trace direction in combination with segment end cells.
* Moved accuflux method from FlwdirRaster to parent Flwdir class.
* Additional `how` argument in fillnodata to indicate how to combine values at confluences. Min, max, sum and mean are supported.

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New
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* Restore FlwdirRaster.inflow_idxs and FlwdirRaster.outflow_idxs methods

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New
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* General Flwdir object for 1D vector based (instead of raster based) flow directions
* flwdir.from_dataframe methods to derive a Flwdir object from a (Geo)DataFrame based on the row index and a column with downstream row indices.
* dem.fill_depressions and pyflwdir.from_dem methods to derive flow directions from DEMs based on Wang & Lui (2015)
* gis_utils.get_edge method to get a boolean mask of valid cells at the interface with nodata cells or the array edge.
* gis_utils.spread2d method to spread valid values on a 2D raster with optional friction and mask rasters
* FlwdirRaster.dem_dig_d4 method to adjust a DEM such that each cell has a 4D neighbor with equal or lower elevation.
* FlwdirRaster.fillnodata method fill nodata gaps by propagating valid values up or downstream.
* region.region_outlets method; which is also wrapped in the new FlwdirRaster.basin_outlets method
* region.region_dissolve method to dissovle regions into their nearest neighboring region
* FlwdirRaster.subbasins_areas method to derive subbasins based on a minimal area threshold

Improved
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* added type="classis" for bottum-up stream order to FlwdirRaster.stream_order, default is type="strahler"
* return subbasin outlet indices for all FlwdirRaster.subbasin* methods
* improved subgrid slope method with optional lstsq regression based slope
* FlwdirRaster.streams takes an optional `idxs_out` argument to derive stream vectors for unit catchments
* FlwdirRaster.streams takes an optional `max_len` argument to split large segments into multiple smaller ones.
* Using the new Flwdir object as common base of FlwdirRaster to share methods and properties
* gis_utils.IDENTITY transform has North -> South orientation (yres < 0) instead of S->N orientation which is in line with flow direction rasters.
* new `restrict_strord` argument in FlwdirRaster.moving_average and FlwdirRaster.moving_median methods to restrict the moving window to cells with same or larger stream order.

Bugfix
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* strahler stream_order method gave incorrect results
* basins.subbasins_pfafstetter reimplementation to fix mall functioning when jitted
* FlwdirRaster.streams fix when called with optional `min_sto` argument

Deprecated
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* FlwdirRaster.main_tributaries method is deprecated due to mallfunctioning when jitted
* FlwdirRaster.inflow_idxs and FlwdirRaster.outflow_idxs

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Improved
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* vectorizing of local flow directions and streams in seperate methods
* fixed subbasins method
* documentation using nbsphinx

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New
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* subbasin_mask_within_region
* contiguous_area_within_region

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Improved
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* IHU upscaling (HESS preprint)