title: How to convert objectid to binary subtype 3 (uuid) with mongodb-erlang and bson-erlang?
body: <p>I generate object ids like this: <code>mongodb_app:gen_objectid()</code>
  This returns obviously a ObjectId type. </p>
  
  <p>I need to have a BinType(3, ...) as we don't store objectids but binary subtype 3 ids. </p>
  
  <p>Does anyone know how to convert this?</p>