Added markdown reference recognition and output to JSON.

pkg/docgen/example/test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * This library is used solely for testing during development and is not
  * intended to be run by the testing machines.
  */
 // TODO(tmandel): Remove this file once docgen is ready for more clear tests.
 library DummyLibrary;
@@ skipping 12 matching lines @@
 
 /**
  * Doc comment for class A.
  */
 /*
  * Normal comment for class A.
  */
 class A implements B {
 
   /**
-   * Markdown _test_ for **class** `A` 
+   * Markdown _test_ for **class** [A] 
    */
   int _someNumber;
 
   A() {
     _someNumber = 12;
   }
 
   int get someNumber => _someNumber;
 
   void doThis(int a) {
     print(a);
   }
 
   int multi(int a) {
     return a * _someNumber;
   } 
 
 }
 
 main() {
   A a = new A();
   print(a.someNumber);
 }
 
 A getA(int testInt, [String testString="default"]) {
   return new A();
 }