Misleading README

It looks like the README has fallen out of sync with the implementation.  If you actually try the example of api.GetUserTimeline(), it doesn't work as expected.

```
>>> user = "bitchinburgers"
>>> print api.GetUserTimeline(user)[0].user.name
u'alexdodge'
```

This seems to be the way to do it:

```
>>> print api.GetUserTimeline(screen_name=user)[0].user.name
u'Bitchin Burgers'
```
