Additional bar chart tests.
Added support for column charts.
Added Line chart support.
Added area chart support.
Added scatter chart support.
Added pie chart support.
Added radar chart support.
Added stock chart support.
Tests for chart axis features.
Added tests for show_blanks_as() chart method.
Added tests for chart area formatting.
Added tests for chart axis crossing.
Added tests for chart drop lines.
Added tests for chart error bars.
Added tests for chart fonts.
Added tests for chart formats.
Added tests for chart gaps.
Added tests for chart gridlines.
Added tests for chart hi-low lines.
Added tests for chart names.