title: Common folder/file structure in Flask app
body: <p>I have just created a flask application and so far I have a router for my "Hello world!" template.</p>
  
  <p>I would like to add a little (a lot) more functionality, but I wonder how I should structure the app directory.</p>
  
  <p>What's the most common way of structuring a Flask app?
  For instance, should I create a <code>routes.py</code> for all my routes?
  Where does the SQLAlchemy stuff go?
  Should models be in <code>models.py</code>?</p>