Django-api-forms

- **Fixed**: Do not return empty error records in `Form:errors`

- **Fixed**: Use custom `DeclarativeFieldsMetaclass` because of custom `Field` class
- **Fixed**: Do not return untouched fields in `Form::payload`
- **Fixed**: Fix for None `default_validators` in `Field`

- **Added**: Support for `validation_{field}` methods in `Form` (initial support)

- **Added**: `EnumField`

- **Added**: First version of `Form` class
- **Added**: `CharField`
- **Added**: `IntegerField`
- **Added**: `FloatField`
- **Added**: `DecimalField`
- **Added**: `DateField`
- **Added**: `TimeField`
- **Added**: `DateTimeField`
- **Added**: `DurationField`
- **Added**: `RegexField`
- **Added**: `EmailField`
- **Added**: `BooleanField`
- **Added**: `RegexField`
- **Added**: `FieldList`
- **Added**: `FormField`
- **Added**: `FormFieldList`