KERI event stream - Service Endpoints

[2byrds]

@swcurran asked several important questions in another PR, about service endpoints in did:webs and the corresponding keri service endpoints. This issue will be resolved with a PR that details did:webs service endpoints, and accurately describes the KERI events related to service endpoints.

Original spec text:
"In KERI, service endpoints are defined by 2 sets of signed data that follow the Best Available Data - Read, Update, Nullify ([[ref: BADA-RUN]]) rules for data processing. The protocol ensures that all data is signed in transport and at rest and versioned to ensure only the latest signed data is available."

Questions from Stephen:
#46 (comment)
I think this should this be “In did:webs service endpoints are defined by 2 sets of signed data using KERI’s Best…."

#46 (comment)
Is this the same for all services in the DIDDoc, or just the KERI services? If just the KERI services, I think it should be in the next section, with this intro section covering all DIDDoc services.

[2byrds]

I need to add examples of the service endpoints that we currently support (witnesses) to the spec.