Make change reason customizable with overriding.

Shortcoming of previous architecture:
Recording reason for change was only through manually setting to each object or through bulk_history_create.
So recording API request as reason automatically was hard to implement with this architecture.

Solution:
Getting change reason is now done through `HistoricalRecords` method `get_change_reason_for_object`.
And thus this method can be overriden in subclass to define custom behavior.

Author: amartis

AUTHORS.rst

@@ -15,6 +15,7 @@ Authors
 - Aleksey Kladov
 - Alexander Anikeev
 - Amanda Ng (`AmandaCLNg <https://github.com/AmandaCLNg>`_)
+- Amartis Gladius (`Amartis <https://github.com/amartis>`_)
 - Ben Lawson (`blawson <https://github.com/blawson>`_)
 - Benjamin Mampaey (`bmampaey <https://github.com/bmampaey>`_)
 - `bradford281 <https://github.com/bradford281>`_

simple_history/models.py

@@ -552,11 +552,18 @@ def post_delete(self, instance, using=None, **kwargs):
         else:
             self.create_historical_record(instance, "-", using=using)
 
+    def get_change_reason_for_object(self, instance, history_type, using):
+        """
+        Get change reason for object.
+        Customize this method to automatically fill change reason from context. 
+        """
+        return get_change_reason_from_object(instance)
+
     def create_historical_record(self, instance, history_type, using=None):
         using = using if self.use_base_model_db else None
         history_date = getattr(instance, "_history_date", timezone.now())
         history_user = self.get_history_user(instance)
-        history_change_reason = get_change_reason_from_object(instance)
+        history_change_reason = self.get_change_reason_for_object(instance, history_type, using)
         manager = getattr(instance, self.manager_name)
 
         attrs = {}