title: Stripe - STPPaymentCardTextField - How to add zip/postal code field?
body: <p>Stripe's iOS SDK's "STPPaymentCardTextField" has only 4 fields for generating a token for a card :
  1. credit card number
  2. expiration month
  3. expiration year
  4. CVC field</p>
  
  <p>Is there another field available for programmatically adding zip/postal code to the STPPaymentCardTextField? </p>
  
  <p>Or should I use a separate textfield(s) to handle additional parameters (and possibly other fields for the STPCard)?</p>