code: function gist (options, callback) {
    if (!options.id) return callback(new Error('missing option: id'))
  
    request({
      url: '/gists/' + options.id,
      qs: {
        access_token: options.token
      }
    }, function (err, json) {
      if (err) return callback(err)
  
      var results = []
  
      async.forEachOf(json.files, function (item, key, callback) {
        processGithubFile({
          item: item,
          key: key,
          json: json
        }, function (err, geojson) {
          if (err) return callback(err)
          if (geojson) results.push(geojson)
          callback(null)
        })
      }, function (err) {
        if (err) return callback(err)
        if (!results.length) return callback(new Error('no geojson found in gist ' + options.id))
        callback(null, results)
      })
    })
  }
docs: get geojson from a gist
  
  @param  {object}   options - id, token (optional)
  @param  {Function} callback - err, data