feat(PieChart): ability to change chart data

@@ -46,6 +46,9 @@
 
 @property (nonatomic, weak) id<PNChartDelegate> delegate;
 
+/** Update chart items. Does not update chart itself. */
+- (void)updateChartData:(NSArray *)data;
+
 - (void)strokeChart;
 
 @end

@@ -169,6 +169,10 @@
     return descriptionLabel;
 }
 
+- (void)updateChartData:(NSArray *)items {
+    self.items = items;
+}
+
 - (PNPieChartDataItem *)dataItemForIndex:(NSUInteger)index{
     return self.items[index];
 }