Fixed an issue where some criteria on the form page wouldn't change to
red or green when one set one of them to 0 in the config. Also added a
lowercase option.
Password validation added, configurable under the [password_validation]
section in config.ini. Each criterion is displayed next to the form, in
red or green depending on whether the password passes it. form.html now
looks different because of it, whether it is enabled or disabled. An
error message is now displayed if the user already exists.
