Function offer_upload 

pub fn offer_upload(
    store: &mut NoteStore,
    pr: &PullRequest,
    poster: &dyn Poster,
    input: &mut impl BufRead,
    out: &mut impl Write,
) -> Result<()>

After a review of a pull request, offers to post its notes there. Lists what would be posted, asks, and posts only on an explicit yes. Posted notes leave the store; notes that fail stay, so nothing is posted twice and nothing is lost.