title: How is endpoint throwing error not callable?
body: <p>I have implemented a basic <code>view.py</code> with below 
      from flask_restplus import Resource, reqparse</p>
  
  <pre><code># the below order matters
  from .auth import auth as auth_blueprint
  app.register_blueprint(auth_blueprint)
  
  parser = reqparse.RequestParser()
  parser.add_argument('email', help = 'This field cannot be blank', required = True)
  parser.add_argument('password', help = 'This field cannot be blank', required = True)
  
  @auth.route('/registration')
  class UserRegistration(Resource):
      def post(self):
          data = parser.parse_args()
          new_user = models.Users(
              email = data['email'],
              password = data['password']
          )
          try:
              new_user.save_to_db()
              return {
                  'message': 'User with email: {} was created.'.format( data['email'])
              }
          except:
              return {'message': 'Something went wrong'}, 500
  </code></pre>
  
  <p>but when  I access the registration endpoint using POST method i get the following error:</p>
  
  <pre><code>TypeError: 'UserRegistration' object is not callable
  </code></pre>