code: function (id, width, height, options, callback) {
              var args = arguments,
                  url,
                  query,
                  retry = false,
                  params,
                  handler;
  
              if (typeof options === 'function') {
                  callback = options;
              } else {
                  options = extend({}, options);
                  retry = options.retry;
              }
  
              retry = (retry === true) && function () {
                  this.getThumbnail.apply(this, args);
              }.bind(this);
  
              params = {
                  width: width,
                  height: height
              };
  
              handler = createResponseHandler(callback, [200, 202], true, retry);
  
              query = querystring.stringify(params);
              url = client.documentsURL + '/' + id + '/thumbnail?' + query;
              return req(url, handler);
          }
docs: Fetches a thumbnail for the given document id
  @param   {string}   id               The document uuid
  @param   {int}      width            The thumbnail width
  @param   {int}      height           The thumbnail height
  @param   {Object}   [options]        Content options
  @param   {boolean}  [options.retry]  Whether to retry the request after 'retry-after' seconds if the retry-after header is sent
  @param   {Function} [callback]       A callback to call with the response (or error)
  @returns {Request}