[OCaml] Add a class example

It is based on the Python class example. The Makefile is based on the
Makefile used in the OCaml shapes example.

Examples/ocaml/class/example.c

@@ -0,0 +1,28 @@
+/* File : example.c */
+
+#include "example.h"
+#define M_PI 3.14159265358979323846
+
+/* Move the shape to a new location */
+void Shape::move(double dx, double dy) {
+  x += dx;
+  y += dy;
+}
+
+int Shape::nshapes = 0;
+
+double Circle::area() {
+  return M_PI*radius*radius;
+}
+
+double Circle::perimeter() {
+  return 2*M_PI*radius;
+}
+
+double Square::area() {
+  return width*width;
+}
+
+double Square::perimeter() {
+  return 4*width;
+}