Rename adix/wstats -> adix/stat

Rename a module to a more general purpose name before much time passes (I already switched from windowed stats terminology to moving stats and the "w" no longer matches); Probably no users yet. ;-)

Also, use the new cligen/strUt.fmtUncertainMerged format. In some strict, technical sense this makes the adix package depend upon cligen, but it is only this one module. So, I am not yet encoding that dep in the nimble file.