In some cases, field classes may be renamed or moved to different

modules. django-evolution had some one-off logic to handle this for when

django itself moved all the fields from django.db.models.fields to

django.db.models, but there was nothing available to consumers of the

library to do the same.
We recently ran into a problem where we decided to remove a dependency

on a third-party field, replacing it with a compatible home-grown

implementation. This worked fine, except django-evolution would fail to

load the signature because the old module didn't exist. This change adds

a new mapping to the django-evolution configuration,

RENAMED_FIELD_TYPES, which allows a project to define their own

renames.

Used this in conjunction with code that set

DJANGO_EVOLUTION['RENAMED_FIELD_TYPES'] to a mapping from our old

  third-party library to our new implementation, and saw that

  django-evolution management commands and Evolver calls worked

  correctly.
Ran unit tests.