Support TRX - Multiple Check Truncated Entries

[bkmoovio]

TRX Multiple Check Truncated Entries - This Standard Entry Class Code is used to identify batches of truncated checks. For more information on check truncation, please see the National Association for Check Safekeeping Guidelines available from NACHA.

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