Allow auditing of entities with many-many relations

The changes made in c619a4e have made
it impossible to load the history of entities that have a many to many
relationship with another entity. I think the old approach of just
providing an empty collection and the notice in the docs is preferable
to not being able to audit the entity at all. Hence I reverted the
change that throws an exception if a many to many relationship is found

src/SimpleThings/EntityAudit/AuditReader.php

@@ -382,7 +382,9 @@ private function createEntity($className, array $data, $revision)
                     $class->reflFields[$assoc['fieldName']]->setValue($entity, $collection);
                 }
             } else {
-                throw new \Exception(sprintf('Association type %d is not yet supported', $assoc['type']));
+                // Inject collection
+                $reflField = $class->reflFields[$field];
+                $reflField->setValue($entity, new ArrayCollection);
             }
         }