0.6.9 January 30 2017

• Added chart trendlines.

0.6.8 January 28 2017

• Added chart error bars.

0.6.7 January 24 2017

• Added chart data labels.

0.6.6 January 22 2017

• Added functions to set chart Up-Down bars: see chart_set_up_down_bars()
  and chart_set_up_down_bars_format() and chart_data_tools.c.
• Added functions to handle blank and hidden data in charts: see
  chart_show_blanks_as() and chart_show_hidden_data().

0.6.5 January 21 2017

• Added functions to set the overlap and gap between series: see
  chart_set_series_overlap() and chart_set_series_gap().

0.6.4 January 20 2017

• Added chart data table option, see chart_set_table() and
  chart_set_table_grid().
• Added Clustered Chart example, see chart_clustered.c.

0.6.3 January 19 2017

• Added chart_set_drop_lines() and chart_set_high_low_lines() functions to
  add chart Drop and High-Low lines to indicate category values.

0.6.2 January 17 2017

• Added chart_series_set_smooth() function to set the line smoothing
  property of a line or scatter chart series.

0.6.1 January 16 2017

• Added option to set formatting for points in a chart. This allow the colors
  of Pie chart segments to be defined.

0.6.0 January 14 2017

• Added option to set the number format for a chart axis, see
  chart_axis_set_num_format().
• Added "invert if negative" option for series fills, see
  chart_series_set_invert_if_negative().