[master] 7767fc32a document event_function change

[Nils Goroll]

commit 7767fc32a368439915086f26ef99cf6aae578484
Author: Nils Goroll <nils.goroll at uplex.de>
Date:   Sat Feb 2 14:51:44 2019 +0100

    document event_function change
    
    Ref d8ae26b5a0b4a1102360a61a145e4730e52d68bc

diff --git a/doc/changes.rst b/doc/changes.rst
index 740906e32..c7c690b1c 100644
--- a/doc/changes.rst
+++ b/doc/changes.rst
@@ -101,6 +101,10 @@ C APIs (for vmod and utility authors)
 * Varnish-based tools using the VUT interface should now consider
   using the ``VUT_Usage()`` function for consistency
 
+* The `event_function` callback for VCL events in vmods used to have
+  the fixed name ``event_function`` and has now been renamed to
+  `$Prefix`\ ``event_function`` if `$Prefix` is defined in the
+  ``.vcc`` files or ``vmod_event_function`` by default
 
 Fixed bugs
 ----------