Update README and OAuth::Lite2::Endpoint::Token

Since you pulled the other one, I did this while working on my implementation.

As before, I believe that this clarifies the intent of the methods. I have based this on the original text and my only aim was to improve readability. I am very open to discussing these changes and providing suggestions.

I have just started using this library, so my reading of these methods may be slightly off. I apologize if that is the case.