ENH TreeModel._register_field():  raise Error when default can't be set
OPT ClusterDist:  multiprocessing
DOC testnd:  better error message for invalid kwargs
ENH ClusterDist:  slices of TFCE results
ENH SourceSpace:  allow .index_for_label() with string
WIP SETUP:  use setuptools upload_docs
ENH t_contrast:  allow cells with "*"