Data security framework for Clojure.

See the GitHub page (esp. Wiki) for info on motivation and design:
  <https://github.com/taoensso/tempel>

See `df.clj` for data formats.
All formats intended to support non-breaking future updates.

Abbreviations:
  External:
    pbkdf - Password Based Key Derivation Function
    aad   - Additional Associated Aata (see `aad-help`)
    akm   - Additional Keying Material (see `akm-help`)
    kek   - Key encryption key (key used to encrypt another key)
    cnt   - Unencrypted content
    ecnt  - Encrypted   content
    kc    - KeyChain
    ck    - ChainKey

  Internal:
      key0  - Rand/user/password key (pre AKM, etc.)
      key1  - Key with AKM, etc.
      key2  - Final key ready for encryption/decryption
      key1b - Backup    key
     ekeyX  - Encrypted key