Dask-ndfilters

* More tests for `_utils`. 30

* Allow Dask to set name for `map_overlap`. 29

* Convert all depths to ints. 27

* Wraps and tests the following SciPy ndimage functions
* convolve
* correlate
* gaussian_filter
* gaussian_gradient_magnitude
* gaussian_laplace
* generic_filter
* laplace
* maximum_filter
* median_filter
* minimum_filter
* percentile_filter
* prewitt
* rank_filter
* sobel
* uniform_filter