Litle: Support optional fields with tokens

* Updated existing token based tests to pass optional fields in the
  options hash.
* Added missing certification tests for explicit token registration.
* Updated existing certification tests to use the latest documented
  data.
* Added support for processing a credit transaction with a token as well
  as a previous transaction id (identification).
* Updated certification specs based on direct feedback from Litle (some
  required data was missing).

Closes #575.