Replace TikZ samples for Asymptote samples

The plot generator is not getting replaced as Asymptote features a much more
powerful module.

.asy/piechart.asy

@@ -0,0 +1,34 @@
+/* Example of use:
+
+access piechart;
+unitsize (70);
+
+int[] values = {1, 2, 3, 2};
+string[] labels = {"a", "b", "c", "very long"};
+
+add(piechart.pie(values, labels, 1.2, green, labelcolor=blue));
+*/
+
+picture pie (int[] values, string[] labels={}, real distance = 0.5, pen color = rgb(1,1,1), pen labelcolor = rgb(0, 0, 0)) {
+	picture opic;
+	// unitsize(100);
+	int total = 0;
+	for (int i: values) {
+		total += i;
+	}
+
+	if (total != 0) {
+		real last = 0;
+		for (int i = 0; i < values.length; ++i) {
+			real current = last+values[i]*360/total;
+			filldraw(opic, arc((0,0), 1, last, current) -- (0,0) -- cycle, values[i]/total * color);
+			if (labels.length == values.length) {
+				// rotate() 0 angle is upwards. We shift it to match the trigonometric circle.
+				label (opic, labels[i], rotate((current+last)/2-90) * (0, distance), labelcolor);
+			}
+			last = current;
+		}
+	}
+	return opic;
+}
+