Altered webworker-child to permit the global worker object to be passed by reference.

[kriskowal]

For some reason, using runInNewContext occludes the worker object, which it would be handy to be able to pass to an API for standard message passing setup.

I've also added a trivial example.

I would like to see the worker run as a module so relative module identifiers can be used inside the worker, relative to the worker file instead of the webworker-child module. This might require node to expose more of its module system primitives though.