Minor spelling fixes & refactoring

I felt like some of the boolean logic in `link.py` was a little cluttered so I tried to reorganize it a bit.
This change was made to match the way `voting_score` is defined in [`builder.py`](https://github.com/reddit/reddit/blob/f373e3cbda3866486c67d33be0a4ecf4107447bc/r2/r2/models/builder.py#L207) and [`subreddit.py`](https://github.com/reddit/reddit/blob/7040139f4685f0960a9f6b3235698f396f6f53ee/r2/r2/models/subreddit.py#L736).