Added changelog, tagged version

CHANGELOG.md

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+# Changelog
+
+## 0.0.2
+
+* Use `valueUri` (which exists in DSTU2+) for FHIR datatypes rather than `valueUrl` (which was introduced after DSTU2)
+* Added `encryptForKeyId` parameter to `$HealthWallet.issueVc` operation, defaulting to absent == no encryption
+* Updated example VC JWT representations to ensure that the `.vc.credentialSubject` contains all subject-specific claims
+* Defined `OperationOutcome` payload for failed `$HealthWallet.issueVc` operations