Add syntax description and example for using a Receipt message to convey the location of an authorization seal (issuance or delegation)

[SmithSamuelM]

Receipt points to Event in authorizor's KEL. Attached to Receipt is source seal triple that is the anchored evet seal to be found at the location pointed to by the reciept. Recipient of this receipt can then verify the authorization seal exists (is valid) and points to the authorized event (either a TEL event ACDC, or a Delegated event). Thus an authorizer can communicate via receipts that it has approved whatever it is authorizing (issuance or delegation) in band with standard KERI messaging. These receipts can be forwarded by other validators. Alternatively, some other validator can source a receipt as needed to provide a reference to an anchoring seal that can then be validated by some other validator.