Update changelog.txt for release 3.4.3-slp.

Author: Anselm Kruis

Stackless/changelog.txt

@@ -4,10 +4,10 @@ Stackless-Python News
 This file documents user visible changes to the Stackless extension of C-Python.
 For other changes see Misc/NEWS.
 
-What's New in Stackless 3.X.X?
+What's New in Stackless 3.4.3?
 ==============================
 
-*Release date: 20XX-XX-XX*
+*Release date: 2017-04-16*
 
 - https://bitbucket.org/stackless-dev/stackless/issues/129
   C-API: Calling PyTasklet_New( NULL, ...) no longer crashes.