DOC MneExperiment:  check that .label_events() returns a Dataset
FIX plot:  find_fig_vlims
ENH plot.Array:  expose `x`, `vmax` and `vmin` arguments
DOC installing
DOC intro
FIX permutation:  sign-flip for n > 32
RF permutation:  iterate over index, not data
API plot.brain:  hide non-public attributes