code: function(imageUrl, callback) {
          readers.getContentsFromUrl(imageUrl.toString(), function(err, data) {
              callback(err, err ? null : data);
          });
  
          return this;
      }
docs: Get the binary data of an image, specified by URL
  
  @param {String}   imageUrl
  @param {Function} callback
  @return {ImboClient}