Usage:
```
$ python scripts/hash_passwords.py --new username admin password
auth_add_p username admin 9415aef5cc5043800377584cff32b90c 26fd308aad6b04f2
```
```
$ python scripts/hash_passwords.py autoexec.cfg
```
updates all instances of `auth_add` to `auth_add_p`.
```
$ python scripts/hash_passwords.py autoexec.cfg \
--new user1 admin password1 \
--new user2 admin password2
```
updates all instances of `auth_add` to `auth_add_p` and adds two new
users.
On Windows, you should be able to drag-and-drop your config file onto
this script and have it automatically updated (not tested).
