Current behavior supports:
- string, rendered as text in response
- object, rendered as JSON object in response

This enhancement enables passing a normal middleware. It allows full customization of the response handling in the case of unauthorized:
```JavaScript
  app.use(basicAuth({
    unauthorizedResponse: function(req, res, next) {
      // use an application's existing error handling stack
      if (req.auth) {
        next(new UnauthorizedError('Login required'));
        return;
      }
      // or send an html page
      if (req.accepts('html') {
        res.render('unauthorized');
        return;
      }
      // or whatever you like!
      res.status(403)
        send({
          message: 'That user will NEVER have access. Ever!'
        });
    }
  }));
```

fixes LionC#23

The typescript check seems out of date, since it's currently failing with hundreds of errors. Further investigation is needed to re-enabe this. Better to disable for now and have the build run successfully on the core codebase.