1. Vault operations created.
2. VaultMetadata classes crated.
3. Copied a fallback from S3 api (TrueOn404OrNotFoundFalseOnIllegalState) this class may require some changes.
4. MessageDigest was removed, AWSRequestSignerV4 is using Guava Hashing now.
5. Some extra changes were made to AWSRequestSignerV4.
6. Added tests for the AsyncClient.
TODO: Response handlers.