Reorganize API wrapper to be more modular

I'd like to make this a bit simpler to use by changing the request format from this style:
```py
sc.get_group_update_comment(group_id=12345, update_id=54321, comment_id=98765)
```
to this:
```py
sc.group(12345).update(54321).comment(98765).get()
```

This would be totally backward-incompatible.