Add filter.rank to __all__ of filter package

skimage/filter/__init__.py

@@ -9,6 +9,7 @@ from ._denoise_cy import denoise_bilateral, denoise_tv_bregman
 from ._rank_order import rank_order
 from ._gabor import gabor_kernel, gabor_filter
 from .thresholding import threshold_otsu, threshold_adaptive
+from . import rank
 
 
 __all__ = ['inverse',
@@ -36,4 +37,5 @@ __all__ = ['inverse',
            'gabor_kernel',
            'gabor_filter',
            'threshold_otsu',
-           'threshold_adaptive']
+           'threshold_adaptive',
+           'rank']