title: How to use use ndb library schemeless
body: <p>using datastore client library.
  Can be used regardless of the state of the datastore property.</p>
  
  <pre><code>datastore_client.put({
    "foo":"foo",
    "bar":"bar",
    "xxx":"xxx", # any property can put
    ...
  })
  </code></pre>
  
  <p>But, using ndb.
  Only predefined properties can be used.</p>
  
  <pre><code>Class Test(ndb.Model):
    foo = StringProperty()
  ...
  Test(
    foo="foo",
    bar="bar" # error
  ).put()
  </code></pre>
  
  <p>If I want to put()/get() schemeless.
  I cannot use ndb?</p>