Add an option to display both absolute and percentage values in pie chart

[MegaChriz]

When you want to draw a pie chart, you have the option to display absolute or percentage values on the chart.

• For displaying a value as absolute you set $Format['WriteValues'] to PIE_VALUE_NATURAL;
• For displaying a value as percentage you set $Format['WriteValues'] to PIE_VALUE_PERCENTAGE;

I'd like to add an option to display both absolute and percentage values on the chart. I propose to display this as follows:

4
(20%)

I propose to set $Format['WriteValues'] to PIE_VALUE_BOTH when you want both absolute and percentage values to be displayed.

I will create a pull request shortly.