Update copyright year.

heading.en.yhtml2

@@ -13,7 +13,7 @@ decl ne is a {
 div id=headline {
     p > YML – Why a Markup Language?!
     div class=small {
-        "YML 2.6.2 of Mo 02 Nov 2019  –  Copyleft 2007-2019, "
+        "YML 2.6.2 of Mo 02 Nov 2019  –  Copyleft 2007-2020, "
         a "http://blog.fdik.org", "Volker Birk";
         " – "
         a "http://fdik.org/yml2.tar.bz2", "Download YML 2";

yml2c

@@ -3,7 +3,7 @@
 
 """\
 YML 2 compiler version 6.2
-Copyleft (c), 2009-2019, Volker Birk  http://fdik.org/yml/
+Copyleft (c), 2009-2020, Volker Birk  http://fdik.org/yml/
 
 """
 

yml2proc

@@ -3,7 +3,7 @@
 
 """\
 YML/YSLT 2 processor version 6.2
-Copyleft (c), 2009-2019 Volker Birk  http://fdik.org/yml/
+Copyleft (c), 2009-2020 Volker Birk  http://fdik.org/yml/
 
 """