Read a body from message_payload and accept data_sm (#84)

* Regression tests for a body in message_payload and for data_sm

* Read a body from message_payload and accept data_sm

* Assert the fixed message_payload and data_sm behaviour against Jasmin

* Record the message_payload and data_sm fixes in the Jasmin findings

* Read an inbound data_sm as the direction it travelled, and export messageOctets

* Refuse a segment with the code its stand-in command defines

* Name the stand-in the refusal status is read from

src/index.ts

@@ -30,6 +30,7 @@ export {
 } from './message.ts';
 
 export { dlrFromPdu, parseReceipt, receiptCodes } from './dlr.ts';
+export { messageOctets } from './message-body.ts';
 export { concatInfo } from './udh.ts';
 export { PduFramer } from './pdu-framer.ts';
 export { uuidv7 } from './uuid.ts';