Django-scrubber

Fixed
- add the same version restrictions on faker to setup.py

Added
- add empty and null scrubbers

Changed
- make `Lorem` scrubber lazy, matching README

Fixed
- set more stringent version requirements (faker >= 3 breaks builds)

Fixed
- correctly clear fake data model to fix successive calls to `scrub_data` (thanks [Benedikt Bauer](https://github.com/mastacheata))

Added
- `Faker` scrubber now supports passing arbitrary arguments to faker providers and also non-text fields (thanks [Benedikt Bauer](https://github.com/mastacheata) and [Ronny Vedrilla](https://github.com/GitRon))

Fixed
- [9](https://github.com/RegioHelden/django-scrubber/pull/9) `Hash` scrubber choking on fields with `max_length=None` - Thanks to [Charlie Denton](https://github.com/meshy)

Added
- Finally added some basic tests (thanks [Marco De Felice](https://github.com/md-f))
- `Hash` scrubber can now also be used on sqlite

Changed
- **BREAKING**: scrubbers that are lazily initialized now receive `Field` instances as parameters, instead of field
names. If you have custom scrubbers depending on the previous behavior, these should be updated. Accessing the
field's name from the object instance is trivial: `field_instance.name`. E.g.: if you have `some_field = MyCustomScrubber`
in any of your models' `Scrubbers`, this class must accept a `Field` instance as first parameter.
Note that explicitly intializing any of the built-in scrubbers with field names is still supported, so if you were
just using built-in scrubbers, you should not be affected by this change.
- related to the above, `FuncField` derived classes can now do connection-based setup by implementing the
`connection_setup` method. This is mostly useful for doing different things based on the DB vendor, and is used to
implement `MD5()` on sqlite (see added feature above)
- Ignore proxy models when scrubbing (thanks [Marco De Felice](https://github.com/md-f))
- Expand tests to include python 3.7 and django 2.1