Add String::online method (to check if we are online and the Url provided is accessible

[DinisCruz]

the String (i.e. @) in this case would be the URL to check (maybe with an optional parameter used to match some content inside the page)

here is an example of where this test would be useful

skip_Tests_If_Offline = (testSuite,next)=>
  url = "https://www.google.com"
  url.GET (html)=>
        if not html
          for test in testSuite.tests
            test.pending = true
        next()