bug fix for when user clicks Cancel at acceptance screen

This library is really great! It's helped me integrate google login in no time!

The only issue I found was (at least in Chrome), if a user went to the 'cancel'/'accept' screen and hit cancel, they would be infinitely redirected back to .../oauth2callback? over and over. I tried many different ways of changing my route and I didn't make any progress. The code looked simple enough, so I just put in a fix that sends data back to the view method, and from there the developer could decide what to do? Below I just redirect the user back to the login view.

Please reject the pull request if you had a better/smarter way to fix this!

Again thanks for all the work so far.

Oh and since I've made use of it recently, I could take some time to flesh out some documentation or add some comments to the example. I had a few other issues I ran into that it might be useful to note in the code..