title: Unable to display serializers.fields on swagger docs
body: <p>I am using <a href="https://pypi.python.org/pypi/django-rest-authemail" rel="nofollow">https://pypi.python.org/pypi/django-rest-authemail</a> for basic email based authentication. 
  While creating swagger docs its working fine with all api which I have created using django models but django-rest-authemail module uses serializers.fields for Login Serializer i.e.</p>
  
  <pre><code>class LoginSerializer(serializers.Serializer):
      email = serializers.EmailField(max_length=255)
      password = serializers.CharField(max_length=128)
  </code></pre>
  
  <p>Hence django-rest-swagger is unable to recognize these fields and failed to load into api docs.
  I have attached the <a href="https://cloud.githubusercontent.com/assets/4718496/6707648/ec1cb630-cd8e-11e4-8880-8932d9029740.png" rel="nofollow">picture</a> for reference.</p>