Fixes to docs - auth tutorial docs were busted!

Hey Tweepy folks,

Here's some fixes to the auth tutorial docs.  I think they were just outdated - they referenced functions, like `set_request_token()`, which didn't exist in the codebase, and were doing odd things with the session token (was a tuple, now a dict?).

Anyhow, setups analogous to this are working well for me.

Thanks for making tweepy!

-Steven