ENH Celltable:  sort data
API test.resample():  _resample -> resample(); iterate only over Y
ENH Celltable:  cat arg to only load certain categories;  testnd.ttest use that
FIX plot:  .set_vlim() methods
FIX dim:  Sensor.neighbors()
ENH data-obj sorting:  `order` kwarg
ENH Celltable:  sort cases (&TEST)
ENH: permutation cluster test for more multidimensional ndvars