### Changed

  - In `derivepassphrase vault`, accept `key` and `phrase` entries just like
    vault(1) does: `key` always overrides `phrase` in the configuration, no
    matter the level.

    This is a command-line only change.
  - In `derivepassphrase vault`, accept falsy values everywhere `vault` does:
    depending on the setting, they are equivalent to zero, the empty string, or
    "not set". ([#17])

    This is a command-line only change.  The API provides a new function to
    normalize falsy settings, but still otherwise requires settings to be of
    the correct type.

[#17]: https://github.com/the-13th-letter/derivepassphrase/issues/17