update release notes

Author: FabianHofmann

doc/release_notes.rst

@@ -1,9 +1,11 @@
 Release Notes
 =============
 
-Upcoming Version
-----------------
+.. Upcoming Version
+.. ----------------
 
+Version 0.4.3
+--------------
 
 * IMPORTANT BUGFIX: The last slice of constraints was not correctly written to LP files in case the constraint size was not a multiple of the slice size. This is fixed now.
 * Solution files that following a different naming scheme of variables and constraints using more than on initial letter in the prefix (e.g. `col123`, `row456`) are now supported.