Add a way to save only dirty fields by default

We create an extra class that can be used when the user wants to always
save only dirty fields when calling save().

src/dirtyfields/__init__.py

@@ -6,6 +6,7 @@
 
 __all__ = ['DirtyFieldsMixin']
 __version__ = "1.9.4.dev0"
-from dirtyfields.dirtyfields import DirtyFieldsMixin
+
+from dirtyfields.dirtyfields import DefaultDirtyFieldsMixin, DirtyFieldsMixin
 
 VERSION = tuple(map(int, __version__.split(".")[0:3]))

src/dirtyfields/dirtyfields.py

@@ -186,10 +186,22 @@ def is_dirty(self, check_relationship=False, check_m2m=None):
 
     def save_dirty_fields(self):
         if self._state.adding:
-            self.save()
+            super().save()
         else:
             dirty_fields = self.get_dirty_fields(check_relationship=True)
-            self.save(update_fields=dirty_fields.keys())
+            super().save(update_fields=dirty_fields.keys())
+
+
+class DefaultDirtyFieldsMixin(DirtyFieldsMixin):
+    """
+    Save dirty fields automatically when calling save()
+    """
+
+    def save(self, *args, save_all=False, **kwargs):
+        if save_all:
+            super().save(*args, **kwargs)
+        else:
+            self.save_dirty_fields()
 
 
 def reset_state(sender, instance, **kwargs):