Fix error handling, extend testcases, add errors to documentation

* Searched for error-codes and had to look into source code
* maybe this is useful ;)
Yeah but you only Export tokenexpired. ;) and you do not use your
jsonwebtoken error at all. So you can check error name.
Am 22.08.2014 15:26 schrieb "Ben Hockey" <notifications@github.com>:

> In index.js:
>
> > @@ -83,7 +83,7 @@ function JsonWebTokenError(message, error) {
> >  JsonWebTokenError.prototype = Object.create(Error.prototype);
> >  JsonWebTokenError.prototype.constructor = JsonWebTokenError;
> >
> > -var TokenExpiredError = module.exports.TokenExpiredError = function (message, expiredAt) {
>
> this provided the ability to use instanceof to check errors. why are you
> not exporting it?
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/auth0/node-jsonwebtoken/pull/20/files#r16597167>.
>