title: Raise KeyError(key) from None in Project
body: <p>I'm experimenting with the use of Huey as a cross platform task queue . I've found <a href="https://github.com/pjcunningham/flask-huey-example" rel="nofollow noreferrer">https://github.com/pjcunningham/flask-huey-example</a> , which I've cloned and set up a virtualenv for using conda. following the readme I tried:</p>
  
  <pre><code>$ python run_app.py
  Traceback (most recent call last):
    File "run_app.py", line 13, in &lt;module&gt;
      app = create_app()
    File "E:\ENVS\r3\hueytest1\app\__init__.py", line 12, in create_app
      _app.config.from_object(os.environ['APP_SETTINGS'])
    File "E:\miniconda2\envs\hueytest1\lib\os.py", line 669, in __getitem__
      raise KeyError(key) from None
  KeyError: 'APP_SETTINGS'
  </code></pre>
  
  <p>I don't see APP_SETTINGS in the project . is this a Flask related env variable? How do I get this working?</p>