TODO:
-Mouse
+Makng subclasses of Mouse::Meta::* immutable breaks the classes.
-* smart exporters
-* method confliction
-* trait mechanism
-* native traits
-
-MouseX
-
-* MouseX::Role::Parameterized
+If one want match_on_type(), it should be supported.
+The 'handles' option for has() is not completely compatible with Moose.