isLog = (obj) => {
    return obj && obj.id !== undefined &&
      obj.clock !== undefined &&
      obj.heads !== undefined &&
      obj.values !== undefined &&
      obj.access !== undefined &&
      obj.identity !== undefined &&
      obj.storage !== undefined
  }
Check if an object is a Log.
@param {Log} obj
@return {boolean}
@memberof module:Log~Log
@instance