Add tasks for all the new languages

Task/Polymorphism/Sidef/polymorphism-1.sidef

@@ -0,0 +1,15 @@
+class Point(x=0, y=0) {
+
+}
+
+class Circle(x=0, y=0, r=0) {
+
+}
+
+func pp(Point obj) {
+    say "Point at #{obj.x},#{obj.y}";
+}
+
+func pp(Circle obj) {
+    say "Circle at #{obj.x},#{obj.y} with radius #{obj.r}";
+}

Task/Polymorphism/Sidef/polymorphism-2.sidef

@@ -0,0 +1,12 @@
+pp(Point.new);              # => Point at 0,0
+var p = Point(1, 2);        # create a point
+pp(p);                      # => Point at 1,2
+say p.x;                    # => 1
+p.y += 1;                   # add one to y
+pp(p);                      # => Point at 1,3
+
+var c = Circle(4,5,6);      # create a circle
+var d = c.clone;            # make a clone of it
+d.r = 7.5;                  # and change the radius to 7.5
+pp(c);                      # => Circle at 4,5 with radius 6
+pp(d);                      # => Circle at 4,5 with radius 7.5