Added "release" task to create a build for CWS. Fixed "archive" task to use content of build/polymer-build.
Fixed log
Workaround https://code.google.com/p/dart/issues/detail?id=14045: Use .dart.precompiled.js instead of .dart.js.
Improved comments. Made "release" task synchronous.
Merge pull request #36 from dinhviethoa/29-archive-release

Build improvement.