Equivalent ID proposal and inferential version pointers

@csuwildcat we chatted about this.

- "657372-1286-6394"
- "block_number-txn_number-entry_number"
- did:example:123

You might use a "ledger pointer" to find a "didUniqueSuffix", and then grab "latest version"

You might use a "ledger pointer" to find a "didUniqueSuffix", and then grab the version at that point in time.

In other words, there can be "aliases" for a did document at a version, and "aliases" for the latest did document.

Sidetree does not officially support the `version` did query param, but we might consider supporting it, and we might consider `sameAs` / `cannonicalId` as they relate to other "aliases"....

I would say we need to be careful about saying "old" === "new" in the sense that compromised rotated keys are authoritative for the latest did document.