Refactor implementation of did:key.

[msporny]

Changed

• BREAKING: Change to named function inputs, key -> keyPair.
• BREAKING: Rename computeKeyId() -> computeId().
• BREAKING: Rename keyToDidDoc() -> keyPairToDidDocument().
• BREAKING: Return {didDocument, keyPairs} from generate().
• Upgrade to crypto-ld 4.0
• Avoid mutation of ed25519 key passed into keyToDidDoc.
• Set id field for keypairs.
• Use underscores for utility functions.

This is being driven by the ezcap work, I'm trying to get to a nice pattern to create the ezcap client:

const baseUrl = 'https://zcap.example/';
const {didDocument, keyPairs} = await didKeyDriver.generate();
const {invocationSigner, delegationSigner} = getCapabilitySigners({didDocument, keyPairs});
const zcapClient = new ZcapClient({baseUrl, invocationSigner, delegationSigner});

[codecov-io]

Codecov Report

Merging #34 (83ffa4d) into master (5d28b0c) will increase coverage by 4.61%. The diff coverage is 97.05%.

@@            Coverage Diff             @@
##           master      #34      +/-   ##
==========================================
+ Coverage   91.30%   95.91%   +4.61%     
==========================================
  Files           2        2              
  Lines          46       49       +3     
==========================================
+ Hits           42       47       +5     
+ Misses          4        2       -2     

Impacted Files	Coverage Δ
lib/Driver.js	95.65% <97.05%> (+4.95%)	:arrow_up:

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[dmitrizagidulin]

This PR has been refactored/re-implemented in PR #35, I propose we close this one.