code: function isDeleted(metadata, rev) {
    if (!rev) {
      rev = winningRev(metadata);
    }
    var id = rev.substring(rev.indexOf('-') + 1);
    var toVisit = metadata.rev_tree.map(getTrees);
  
    var tree;
    while ((tree = toVisit.pop())) {
      if (tree[0] === id) {
        return !!tree[1].deleted;
      }
      toVisit = toVisit.concat(tree[2]);
    }
  }
docs: check if a specific revision of a doc has been deleted - metadata: the metadata object from the doc store - rev: (optional) the revision to check. defaults to winning revision