title: How to backup datastore with filter
body: <p>I declare table on datastore,
  such as  |id|date|value1|value2|...|</p>
  
  <p>I want to backup only this week.("date > today-7" and "date &lt; today")</p>
  
  <p>Can I backup with filtering?
  (Datastore Admin or something.)</p>