code: function base64(url, obj, _, fn){
    if (3 == arguments.length) fn = _;
    var prefix = exports.prefix;
    obj = encode(JSON.stringify(obj));
    obj = encodeURIComponent(obj);
    url += '?' + prefix + '=' + obj;
    jsonp(url, { param: exports.callback }, function(err, obj){
      if (err) return fn(err);
      fn(null, {
        url: url,
        body: obj
      });
    });
  }
docs: Send the given `obj` to `url` with `fn(err, req)`.
  
  @param {String} url
  @param {Object} obj
  @param {Function} fn
  @api private