Updated io article for Dart SDK version 0.4.3.1_r20444
Merge pull request #51 from financeCoding/fix_io_article

Updated io article for Dart SDK version 0.4.3.1_r20444
clean up example code

BUG=

Review URL: https://chromiumcodereview.appspot.com//12656009
add Numbers, JSON, URIs to cookbook

Review URL: https://chromiumcodereview.appspot.com/12942021