First draft for web workers' support
Queue events when entangled port is local
A port is sent with its message queue
Rename data to event
Code cleaning
Add Worker.postMessagePorts for non polyfilled environment
Improve browser compatibility for setOnMessage
When targetOrigin to "*", the origin on the event object is "null"
Allows message ports to be pass through a user agent
Sample to pass a port from a grand parent window to a grand child iframe
Create sample project for web worker
Refactor code

* Integration tests for worker and iframe
* `MessagePort.start` dispatches events asynchronously
* Message.encodeEvent
* Rename MessageChannel.postMessage to Window.postMessage
* Worker.postMessage