Exchange sparkline

The exchange's volume sparkline series for a period (defaults to 7d) — the same series the web's exchange rows render.

points is a sample of at most 480 readings, oldest first, each a volume at an ISO-8601 time. low and high are the true extremes of the whole period — they bound every point, but need not appear among the sampled ones. change is the move across the period in PERCENT (1.25 means +1.25%).