Add config option to consider that "comment" reviews request changes

[bnjbvr]

Plus a few cleanups.

This is an attempt to fix #11: there's an optional additional configuration option that makes it possible to consider a "comment" review as a "request-change" review.

Pros:

• a reviewer who adds a "comment" review doesn't get their review request invalidated. They have to explicitly approve the PR to get up to that point.

Cons:

• a drive-by review "comment" can be blocking a PR from getting merged. In this case, I would think that if someone randomly did a drive-by review of my code, it would be legitimate to ask them for formal review thereafter, and get their approval. So that doesn't seem too unreasonable, and we can try it out and see if it's too often a problem or not.

[repi]

• a drive-by review "comment" can be blocking a PR from getting merged. In this case, I would think that if someone randomly did a drive-by review of my code, it would be legitimate to ask them for formal review thereafter, and get their approval. So that doesn't seem too unreasonable, and we can try it out and see if it's too often a problem or not.

Think have run into this before but I don't remember the context/repo, the draw back of that was that compared to reviewers, you can't remove a user that added a comment that is blocking.

Still think this is a decent approach and tradeoff though to try it out