Xontrib-history-encrypt

Typo fixed.

Added `dummy` encryptor.

The best encryption of the data when there is no the data. The dummy encryptor stores command only in the memory during the session without saving it on the disk. After the end of the session the commands will be lost.

python
Add to xonsh RC file
$XONSH_HISTORY_ENCRYPTOR = 'dummy'
xontrib load history_encrypt

* Added setting `600` (`-rw------`) permission to the history file.
* Added debug mode: `$XONSH_HISTORY_ENCRYPT_DEBUG = True`

Added setting the strict permissions for the history file (`chmod 0600`).

* Added Fernet encryptor
* New README

Added the implementation of Fernet (AES CBC + HMAC) to the README.