Update API docs and demos for recent worker improvements.

Cross-origin scripts in workers is forbidden by the [spec](http://www.w3.org/TR/workers/#dedicated-workers-and-the-worker-interface), so there is no confusion:

>4.8.2 Dedicated workers and the Worker interface
If the origin of the resulting absolute URL is not the same as the origin of the entry script, then throw a SecurityError exception.

However the spec doesn't forbid scripts from a subdomain, neigther blob-urls. Term "URL" it more accurate here because we *actually* interpret these options as URLs. "Path" could imply that some special charaters (e.g. space) are allowed, which is not true.