v3

Will keep this in a branch called v3 until we've discussed various aspects of it.

In summary, 

- Promises based interface
- Singleton
- Returns an article model

```
var ft = require('../lib2/api')('xxx');
ft
  .get('03b49444-16c9-11e3-bced-00144feabdc0')
  .then(function (article) {
    console.log(article.body);
});
```