Add sample sizes styled by default locale.
Estimate datastore disk space instead of store capacity.

The store capacity estimate included a lot of approximate numbers which
made it very much a guess. This excludes outliers before averaging.
Add --hourly to analyze up to the current hour.

Midnight is desirable for longer-term things like the gnuplot plots that
take a day of data, but the RRDTool estimates are hourly so updating
hourly is convenient.