1.17: Allow control over font size (#10), by @drewnoakes
 *        Timestamp text won't overlap, by @drewnoakes
 * v1.18: Allow control of max/min label precision, by @drewnoakes
 *        Added 'borderVisible' chart option, by @drewnoakes
 *        Allow drawing series with fill but no stroke (line), by @drewnoakes
 * v1.19: Avoid unnecessary repaints, and fixed flicker in old browsers having multiple charts in document (#40), by @asbai
 * v1.20: Add SmoothieChart.getTimeSeriesOptions and SmoothieChart.bri