update examples on homepage

src/tests/site/code/syntax.dart

+import 'dart:math' as math;            // Importing a library.
+
+// Functions and variables can be inside or outside of classes.
+var _shapes = new List();             // A global variable.

[sethladd, 2013/08/09 01:45:22]

I think we can drop the _, as I wonder if it's too much here. I couldn't find an
example of you explaining the _.

Your call.

[Kathy Walrath, 2013/08/12 18:30:56]

Done.

+addShape(shape) => _shapes.add(shape); // Function shorthand syntax: =>
+
+class Ellipse extends Shape {         // Declaring a class.
+  num major = 0;                       // An instance variable (property).
+  num minor = 0;
+  static const _C = math.PI/4;        // A constant.
+  num get area => _C*major*minor;      // A property implemented with a getter.
+
+  Ellipse(this.major, this.minor);     // Compact constructor syntax.
+  Ellipse.golden(this.major) {         // A named constructor.
+    minor = major*(1 + math.sqrt(5))/2;
+  }
+  
+  // HIDE THIS: Overriding Object's toString() method.
+  String toString() => 'Ellipse: ${major}x${minor} ($area); rotation: $rotation; $color';
+}
+
+// Every app has a main() function, where execution starts.
+main() {
+  print(new Ellipse.golden(1));
+  
+  // The cascade operator (..) saves you from repetitive typing.
+  addShape(new Ellipse.golden(10)..minor *= 2
+                                 ..rotation = 20
+                                 ..color = 'rgb(0,129,198)');
+  
+  print(_shapes[0]);
+}
+
+abstract class Shape {
+  num get area;
+  num rotation = 0;
+  String color = 'black';
+}