Make rating a decimal field

bookwyrm/models/fields.py

@@ -444,3 +444,7 @@ class BooleanField(ActivitypubFieldMixin, models.BooleanField):
 
 class IntegerField(ActivitypubFieldMixin, models.IntegerField):
     """ activitypub-aware boolean field """
+
+
+class DecimalField(ActivitypubFieldMixin, models.DecimalField):
+    """ activitypub-aware boolean field """

bookwyrm/models/status.py

@@ -273,11 +273,13 @@ class Review(Status):
     book = fields.ForeignKey(
         "Edition", on_delete=models.PROTECT, activitypub_field="inReplyToBook"
     )
-    rating = fields.IntegerField(
+    rating = fields.DecimalField(
         default=None,
         null=True,
         blank=True,
         validators=[MinValueValidator(1), MaxValueValidator(5)],
+        decimal_places=2,
+        max_digits=3,
     )
 
     @property