Adding a method to update stories

@thegrubbsian why isn't the update in the context of the Story object.

```
project  = client.project(123456)
story = project.story(847762630) 
story.attributes = { :name => 'Jane' }
story.save
```

or wrap setting the attributes and saving in an update method.

```
story.update(:name => 'Jane')
```

Seems more intuitive that you would get an existing Story, change some data, and then save.