ENH data-objects:  ADD .std()
ENH ClusterDist:  dist_dim

collect permutation maxima distribution for all values of one dimension
ENH ClusterDist:  dist_tstep
ENH ClusterDist:  allow arbitrary dist_dim
WIP ClusterDist:  flexible tfce-probability map
WIP ClusterDist:  work with multidimensional dist
FIX ClusterDist:  finalize
API NDVar:  index for mne label

old: SourceSpace.label_index -> array
new: SourceSpace.index_for_label -> NDVar
ENH SourceSpace:  add parcellation
ENH Celltable:  ADD .data_for_cell() with advanced cell names
AMD WIP test-class
FIX Dataset.__setitem__:  order of key and :
WIP res class
TEST TestResult:  persistence
WIP res class
FIX ClusterDist:  persistence