TEST:  add some tests
ENH WxTerm:  don't print invalid interpreter intro
ENH Makefile:  add `clean-py` option to remove *.pyo and *.pyc files
ENH Factor:  sort .cells naturally
FIX plot.utsnd:  x-axis in ms
FIX plot.TopoButterfly:  remove stray "t = 0" label
EXA:  simple meg
ENH:  combine NDVars with SourceSpace dim
DOC
WIP DOC