title: Storing in BlobKeyProperty
body: <p>I have a model with a field called <code>testblob</code> which is a <code>BlobKeyProperty</code>.
  I know that I need to store the data in a Blob, then get the key and save the key in my model's field <code>testblob</code>, but I can't understand the WebApp2 docs. They are missing an example, or I just can't see it.
  How can I save a blob?</p>