RLS: Release 5.3.0

Finalize for releae 5.3.0

Author: bashtage

doc/source/changes/5.0.txt

@@ -2,10 +2,12 @@
 Version 5
 =========
 
-Changes Since 5.2
-=================
+Release 5.3
+===========
 - Fixed a bug in :func:`~arch.univariate.mean.arch_model` where ``power`` was
   not passed to the :class:`~arch.univariate.FIGARCH` constructor (:issue:`572`).
+- Fixed a bug that affected downstream projects due to an overly specific assert
+  (:issue:`569`).
 
 Release 5.2
 ===========