title: Create comment on pull request
body: <p><a href="http://developer.github.com/v3/pulls/comments/" rel="noreferrer">GitHub's comment API</a> seems to allow you to create comments on a pull request, but only if you supply a specific line number in the diff to comment on.  Is there a way to create a comment on the pull request as a whole, the equivalent of typing at the bottom of the pull request screen in GitHub's web interface?</p>