title: Flask-Restless dumps Decimal value from Flask-Sqlalchemy
body: <p>i have this model using Flask-SQLAlchemy:</p>
  
  <pre><code>class Menu(Document, db.Model):
      id = db.Column(db.Integer, primary_key=True, autoincrement=True)
      name = db.Column(db.String(80), unique=True, index=True)
      price = db.Column(db.Numeric)
  </code></pre>
  
  <p>and i can create api using Flask-Restless for this model. The problem is when i HTTP GET from the api url:</p>
  
  <pre><code>  File "/usr/lib/python2.6/json/encoder.py", line 344, in default
      raise TypeError(repr(o) + " is not JSON serializable")
  TypeError: Decimal('10000.0000000000') is not JSON serializable
  </code></pre>
  
  <p>The problem is obvious the JSON encoder cannot encode Decimal value which is mapped to price (Numeric column type). Is there any workaound to enable Flask-Restless using custom JSON encoder?</p>