introduce 3.1 and 4.0 upgrade files

Author: xabbuh

UPGRADE-3.1.md

@@ -0,0 +1,30 @@
+UPGRADE FROM 3.0 to 3.1
+=======================
+
+DependencyInjection
+-------------------
+
+ * Using unsupported configuration keys in YAML configuration files has been
+   deprecated and will raise an exception in Symfony 4.0.
+
+ * Using unsupported options to configure service aliases has been deprecated
+   and will raise an exception in Symfony 4.0.
+
+Form
+----
+
+ * The `choices_as_values` option of the `ChoiceType` has been deprecated and
+   will be removed in Symfony 4.0.
+
+Serializer
+----------
+
+ * Passing a Doctrine `Cache` instance to the `ClassMetadataFactory` has been
+   deprecated and will not be supported in Symfony 4.0. You should use the
+   `CacheClassMetadataFactory` class instead.
+
+Yaml
+----
+
+ * The `!!php/object` tag to indicate dumped PHP objects has been deprecated
+   and will be removed in Symfony 4.0. Use the `!php/object` tag instead.

UPGRADE-4.0.md

@@ -0,0 +1,28 @@
+UPGRADE FROM 3.x to 4.0
+=======================
+
+DependencyInjection
+-------------------
+
+ * Using unsupported configuration keys in YAML configuration files raises an
+   exception.
+
+ * Using unsupported options to configure service aliases raises an exception.
+
+Form
+----
+
+ * The `choices_as_values` option of the `ChoiceType` has been removed.
+
+Serializer
+----------
+
+ * The ability to pass a Doctrine `Cache` instance to the `ClassMetadataFactory`
+   class has been removed. You should use the `CacheClassMetadataFactory` class
+   instead.
+
+Yaml
+----
+
+ * The `!!php/object` tag to indicate dumped PHP objects was removed in favor of
+   the `!php/object` tag.