NewCommenter creates a Commenter for updating PR with comments.

AbuseRateLimitError return when the GitHub abuse rate limit is hit.

CommentAlreadyWrittenError returned when the error can't be written as it already exists.

Commenter is the main commenter struct.

CommentNotValidError returned when the comment is for a file or line not in the pr.

PRDoesNotExistError returned when the PR can't be found, either as 401 or not existing.