Player activity by band

Whether each band of the region's players is still playing, as a daily series. The histograms on /players/distribution count how many accounts reached a level; this counts how many of them turned up, which is the only way to tell a thriving band from a large dormant one. Rates should be read against observed (accounts actually read inside the window) rather than against players, since an account nobody read is not known to be idle. Recorded hourly and keyed by UTC day, so the newest day is still refining. The series cannot be backfilled: every counter is measured relative to the instant it was read. 404 until the first run. Dates are ISO 8601 strings.