0.5.9 January 14 2017

• Added support for chart axis crossing. See chart_axis_set_crossing() and
  chart_axis_set_crossing_max().

0.5.8 January 13 2017

• Added chart_axis_set_major_tick_mark() and
  chart_axis_set_minor_tick_mark() functions to chart axis tick marks.

0.5.7 January 12 2017

• Added chart_axis_set_display_units() function to set chart axis display
  units.

0.5.6 January 11 2017

• Added chart_axis_set_interval_unit() and chart_axis_set_interval_tick()
  functions to adjust category axis intervals.

0.5.5 January 10 2017

• Added chart_axis_set_major_unit() and chart_axis_set_minor_unit() to set
  the major and minor units of a category axis.

0.5.4 January 9 2017

• Added chart_axis_set_label_position() option to position the axis labels
  (numbers).

0.5.3 January 8 2017

• Added chart_axis_set_position() option to position a category axis
  horizontally on, or between, the axis tick marks.

0.5.2 January 7 2017

• Added option to turn off chart axis: chart_axis_off().

0.5.1 January 6 2017

• Added chart major and minor gridlines handling, see:
  • chart_axis_major_gridlines_set_visible()
  • chart_axis_minor_gridlines_set_visible()
  • chart_axis_major_gridlines_set_line()
  • chart_axis_minor_gridlines_set_line()

0.5.0 January 5 2017

• Added chart and plot area formatting. See chart_chartarea_set_line() and
  chart_plotarea_set_line().