[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.h

@@ -0,0 +1,34 @@
+/* File : example.h */
+
+class Shape {
+public:
+  Shape() {
+    nshapes++;
+  }
+  virtual ~Shape() {
+    nshapes--;
+  }
+  double  x, y;
+  void    move(double dx, double dy);
+  virtual double area() = 0;
+  virtual double perimeter() = 0;
+  static  int nshapes;
+};
+
+class Circle : public Shape {
+private:
+  double radius;
+public:
+  Circle(double r) : radius(r) { }
+  virtual double area();
+  virtual double perimeter();
+};
+
+class Square : public Shape {
+private:
+  double width;
+public:
+  Square(double w) : width(w) { }
+  virtual double area();
+  virtual double perimeter();
+};