DOC/STY: weightstats: work on docstrings, some pylint cleanup
REF: rename method, add to returns
ENH/REF: add tost method to DescrStatsW, privatize 2 functions, change in a return
ENH: add power for t-tests, initial commit (script file)
REF: cleanup initial script, remove experimental parts
ENH/TST add backup to fsolve, add tests against R:pwr