code: function Cache(ttl, dir) {
      // This cache will live forever if ttl is null
    if (typeof ttl !== 'number') {
      ttl = null;
    }
    this.ttl = ttl;
    this.dir = dir;
  }
docs: /*
  @param {Number} ttl - how long to store a value. null will store forever
  default: null
  @param {String} dir - Where to store data