Implement GitHub.API.Repository.comments #1111
Description
Problem
We can fetch all comments for a repository, instead of dealing with individual issues. Due to pagination and the fact that most issues have less than a page of comments, fetching from repositories would save up on request count and reduce the chance of hitting the rate limits.
https://developer.github.com/v3/issues/comments/#list-comments-in-a-repository
Blocked by #1131