title: Serialize/deserialize FLAGS in Tensorflow
body: <p>I want to serialize my tensorflow configuration flags so they're stored in a file and I can reload them later.
  The json module objects to serializing the 'Flag' type. I tried constructing a new dictionary using the flag <code>name</code> and <code>FLAGS.__flags[name].value</code> but some flags are nested dictionaries.
  It seems like I'm trying to reinvent the wheel.  Is there a concrete example of serializing/deserializing the config?</p>
  
  <p><code>TypeError: Object of type 'Flag' is not JSON serializable</code></p>