v0.6.0: Import & export for AES and mixed keys.

v0.6.0: Import & export for AES and mixed keys.

    - GH Actions on Windows/macOS
    - Add argcomplete (optional end-user add-on).
    - Add fixes & tests for master password.

    - tests: Generate mixed key test data. Use some mocks.
    - tests: Avoid modifying .json files, use temp storage.
    - tests: Add test for AES export/import (AES, 3DES, and mixed keys).

    - Tidy up, lint, and format.
    - Fix edge cases with argcomplete.
    - Windows: Fix profile discovery and CSV printing.
    - Better loop logic (for imports w/ empty row or missing header).

    - Config files.
    - Add stuff back that was removed accidentally in a frenzy.