Allow overriding of messages

[mic159]

Add code for use as a field validator

Set the code of the ValidationError for pwned passwords to pwned_password, to allow the use of error_messages when used in a field as a regular validator.

See: https://docs.djangoproject.com/en/2.0/ref/forms/validation/#raising-validationerror
See: https://docs.djangoproject.com/en/2.0/ref/forms/fields/#error-messages

Example:

def pwned_validator(password):
    PwnedPasswordsValidator().validate(password)

class ChangePassword(forms.Form):
    forms.CharField(
        validators=[pwned_validator],
        error_messages={
            'pwned_password': 'Example message',
        }
    )

Override messages in Django settings

Unfortunately you cannot override messages like the above when used in a clean_* method (like the default Django change password form).
So I also added a way to override it in the OPTIONS of the validator in the settings.
You can also put the number of times the password appeared in breaches with the %(amount)d syntax, and even an optional plural form.

For example:

{
    'NAME': 'pwned_passwords_django.validators.PwnedPasswordsValidator',
    'OPTIONS': {
        'error_message': 'That password was pwned',
        'help_message': 'Cannot be pwned password',
    },
}

With count (and plural form):

{
    'NAME': 'pwned_passwords_django.validators.PwnedPasswordsValidator',
    'OPTIONS': {
        'error_message': (
                'Pwned %(amount)d time',
                'Pwned %(amount)d times',
        ),
    },
}

[ubernostrum]

I need to think a bit on this one. Still digging out from under post-PyCon pile of stuff to read.

[ubernostrum]

Now that the package reorg branch has landed and the code lives in src/, do you mind rebasing this to have the files in the correct locations?

[mic159]

@ubernostrum It is now rebased

[jessexoc]

@ubernostrum Are there plans to push a new release to PyPI soon?