Major refactor, implement general DidDocument class.

[dmitrizagidulin]

• Replace DidIo class with CachedResolver.
• Breaking change in generate() / init() signature. Keys are now no longer stored on the DidDocument instance itself. generate() returns a tuple of {didDocument, keyPairs, methodFor}.
• Add tests.

[mattcollier]

watching: https://github.com/digitalbazaar/bedrock-edv-storage/issues/2

[mattcollier]

@dmitrizagidulin Can you provide a status update on this PR?

[mattcollier]

@dmitrizagidulin Can you provide a status update on this PR?

[dmitrizagidulin]

@mattcollier currently working on it (as part of the crypto-ld v4 / minimal-cipher series of propagations).

[mattcollier]

NOTE: it appears the buildDocumentLoader API described here has not yet been implemented.

https://github.com/digitalbazaar/did-io/tree/v0.9.x#using-cachedresolver-as-a-documentloader

[dmitrizagidulin]

@mattcollier

NOTE: it appears the buildDocumentLoader API described here has not yet been implemented.

Ahh right, haven't gotten to that yet. If that's something that's interesting, I can probably implement it tomorrow?

[dmitrizagidulin]

Update on buildDocumentLoader() function - removed from this PR, deferred to issue #56.