Drf-writable-nested

* Related objects are not deleted if they have relation with on_delete=SET_NULL/SET_DEFAULT 72 (izimobil)

* Support django 4.0 and python 3.10 160 (johnthagen)
* Documentation update 148 (xalien10)
* Fix reverse m2m relation update 167 (bierik)

* Support django 3.2 and python 3.9 142
* Make nested object deletion extensible 143 (kavdev)
* Support extended validator with message and other props for UniqueFieldsMixin (starryrbs)

* Fix: Refresh from DB when updating nested object 122 (pcarn)
* Fix: UniqueFieldsMixin validation optional for partial update 117 (robinchow)
* Add Django 3.1 to CI tests (johnthagen)

* Add support for Django 3.1 115 (LeeHanYeong)

* Drop end-of-life Django versions, add Django 2.2 and 3.0, and Python 3.8 (johnthagen)