Add a simple python OAuth example using requests-oauthlib.

A [fully working example](https://gist.github.com/ib-lundgren/6507798) of how to get an OAuth 2 token for a GitHub user and use it to fetch a user profile. It uses the Flask web framework but should be easily transferable to other frameworks. Unlike the current example it uses the [requests-oauthlib](https://github.com/requests/requests-oauthlib) library.