added front page samples to testing, plus a couple of tweaks to front page and code lab

src/tests/site/code/syntax.dart

-import 'dart:math';                   // Import a library.
+import 'dart:math' show PI;
 
+List shapes = [];                     // Use literals to create lists.
+addShape(shape) => shapes.add(shape); // Function shorthand syntax.
+
+main() {  
+  // The cascade operator (..) saves you from repetitive typing.
+  addShape(new Ellipse(10, 20)..rotation = 45*PI/180
+                              ..color = 'rgb(0,129,198)'
+                              ..outlineWidth = 0);
+  
+  // You can easily insert expression values into strings.
+  print('Area of the first shape: ${shapes[0].area}');
+}
+
 abstract class Shape {
   num get area;
   num rotation = 0;
   num outlineWidth = 1;
   String color = 'black';
 }
 
-class Ellipse extends Shape {              // Declare a class.
-  num majorAxis = 0;                       // An instance variable (property).
-  num minorAxis = 0;
+class Ellipse extends Shape {
+  num minorAxis, majorAxis;
+
+  // Syntactic sugar to set members before the constructor body runs.
+  Ellipse(this.minorAxis, this.majorAxis);
+
   static const num C = PI/4;              // A constant.
-  num get area => C*majorAxis*minorAxis;   // A property implemented with a getter.
+  num get area => C*majorAxis*minorAxis;  // A property implemented with a getter.
 
-  Ellipse(this.majorAxis, this.minorAxis); // Compact constructor syntax.
-  Ellipse.circle(diameter) {               // A named constructor.
+  Ellipse.circle(diameter) {              // A named constructor.
     minorAxis = majorAxis = diameter;
   }
   
   // Override Object's toString() method.
   String toString() =>
       'Ellipse: ${majorAxis}x${minorAxis} ($area); rotation: $rotation; $color';
 }
-
-// Functions and variables can be inside or outside of classes.
-var shapes = new List();              // A global variable.
-addShape(shape) => shapes.add(shape); // Function shorthand syntax.
-
-// Every app has a main() function, where execution starts.
-main() {  
-  // The cascade operator (..) saves you from repetitive typing.
-  addShape(new Ellipse(10, 20)..rotation = 45*PI/180
-                              ..color = 'rgb(0,129,198)'
-                              ..outlineWidth = 0);
-  
-  // Convert expressions to strings using ${...}.
-  print('Area of the first shape: ${shapes[0].area}');
-  print(shapes[0]);
-}