whatsnew: Message.set_param *replace*, Policy.content_manager.

Also cleaned up the email section and fixed some markup bugs in the
email docs.
diff --git a/Doc/library/email.policy.rst b/Doc/library/email.policy.rst
index c2f9e6a..97358f0 100644
--- a/Doc/library/email.policy.rst
+++ b/Doc/library/email.policy.rst
@@ -419,7 +419,7 @@
       additional arguments.  By default ``content_manager`` is set to
       :data:`~email.contentmanager.raw_data_manager`.
 
-      .. versionadded 3.4
+      .. versionadded:: 3.4
 
 
    The class provides the following concrete implementations of the abstract