code: function cat(uri, callback) {
    if (!uri) {
      callback(new Error('URI is required'))
    }
    util.get(uri, function(err, val, uri) {
      callback(null, val, uri)
    })
  }
docs: cat gets the turtle for a uri
  @param  {string}   uri      The URI to get
  @param  {Function} callback Callback with text and uri