rename 'deleted' to 'deleted_on'

[SarunasAzna]

deleted field is a DateTimeField therefore I suggest to add _on to its name so it would be clear that it is DateTimeField. Now you could interpret it as BooleanField (it is BooleanField on version 0.3.x)
Apparently there is no Django convention for Date/DateTimeField so the suggestions is based with:

1. Over frameworks conventions.
2. Zen of Python mantra - Explicit is better than implicit. (DateTime/Boolean confusion violates that)
3. Complicated app migrations (0.3x to 0.4.x and newer)

[Gagaro]

We should keep that in mind for the next major version. It would have make migrations less painful indeed.

[theY4Kman]

I love this! Since I'm looking to replace django-softdelete during an upgrade to Django 2.0, I might try my hand at this and submit a PR.

One suggestion, though: "deleted_at" vs "deleted_on", for DateTimeField vs DateField.

Row 456 was deleted on January 23, 2017

Row 456 was deleted at 8:37, January 23, 2017

[tombreit]

This feature seems to be already implemented and documented in the top level README.rst: and on RTD via the setting SAFE_DELETE_FIELD_NAME. Mentioned also in #162 .

[Gagaro]

Indeed, it is now configurabled.