STY data_obj
FIX NDVar:  source space connectivity
FIX NDVar:  always copy() inherited info dicts
ENH NDVar:  indexing with boolean NDVar
ENH NDVar:  new methods: any, max, mean, min
FIX NDVar:  indexing into source space that results in no connectivity
FIX NDVar:  SourceSpace connectivity
ENH data-objects:  `.abs()` method for Var and NDVar
ENH testnd:  compute clusters without permutation
ENH cluster tests: implement advanced cluster properties as Dimension methods

- FIX tmin criterion with non-adjacent dimensions
ENH  load.besa.dat_set():  allow * in path
ENH Factor:  add `.endswith()` method
ENH _ClusterDist.__repr__()
ENH combine():  Datasets inherit info (intersection)