pagination in listIssueComments

I need to fetch all comments (>50) in an issue, but I don't know how to pass params like
```js
{
per_page: 100,
page: 2
}
```
to [`listIssueComments`](https://github.com/michael/github/blob/master/lib/Issue.js#L65).

I also find that there is a method called `_requestAllPages`, but only applied to [`listIssues`](https://github.com/michael/github/blob/master/lib/Issue.js#L43).

Is is better to add options params or use `_requestAllPages` in `listIssueComments`?

Thanks a lot.

Start by reading lib/Issue.js at listIssues, listIssueComments, and _requestAllPages to understand the existing pagination entry points. Check how listIssueComments is called and documented, then define a consistent way for callers to retrieve more than one page of comments and verify that the behavior is clear from the public API.

由索引模型根据 Issue 内容生成。