Rename samples subdirectories

samples/Dart/point.dart

@@ -0,0 +1,15 @@
+class Point {
+  Point(this.x, this.y);
+  distanceTo(Point other) {
+    var dx = x - other.x;
+    var dy = y - other.y;
+    return Math.sqrt(dx * dx + dy * dy);
+  }
+  var x, y;
+}
+
+main() {
+  Point p = new Point(2, 3);
+  Point q = new Point(3, 4);
+  print('distance from p to q = ${p.distanceTo(q)}');
+}