Finishing touches and code clean-up before final review

* Reverted hard-wired library dependencies on lib-cov.  Correct behavior
  has been observationally confirmed, so it's time to wrap things up and
  put things back in order.

  As a feature-request, rch requested that we integrate Rewire into
  Whiskey to better support this kind of testing, where we want to use
  the examples with code-coverage.

* Fixed many missing "global variable" leaks.

* Fixed style issues, such as " vs ' for strings.

* Removed unused references to fs module and fs.appendFileSync().

* I believe I did the right thing to list Istanbul as a proper npm
  dependency for Whiskey.