Support ADV - Automated Account Advice SEC code

[wadearnold]

ADV - Automated Accounting Advice - This Standard Entry Class Code represents an optional service to be provided by ACH operators that identifies automated accounting advices of ACH accounting information in machine readable format to facilitate the automation of accounting information for participating DFIs.

• Library should support the reading and writing of ADV records.
• Document the ADV record format on the documentation website.
• Create a test example for the reading and writing of ADV records