various: update copyright year

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>

Markdown.pl

@@ -4,7 +4,7 @@
 # Markdown -- A text-to-HTML conversion tool for web writers
 #
 # Copyright (C) 2004 John Gruber
-# Copyright (C) 2015,2016,2017,2018,2019,2020 Kyle J. McKay
+# Copyright (C) 2015,2016,2017,2018,2019,2020,2021 Kyle J. McKay
 # All rights reserved.
 # License is Modified BSD (aka 3-clause BSD) License\n";
 # See LICENSE file (or <https://opensource.org/licenses/BSD-3-Clause>)
@@ -22,7 +22,7 @@ use vars qw($COPYRIGHT $VERSION @ISA @EXPORT_OK);
 
 BEGIN {*COPYRIGHT =
 \"Copyright (C) 2004 John Gruber
-Copyright (C) 2015,2016,2017,2018,2019,2020 Kyle J. McKay
+Copyright (C) 2015,2016,2017,2018,2019,2020,2021 Kyle J. McKay
 All rights reserved.
 ";
 *VERSION = \"1.1.11-PRE"
@@ -3573,7 +3573,7 @@ BEGIN {
 /* <![CDATA[ */
 
 /* Markdown.pl fancy style sheet
-** Copyright (C) 2017,2018,2019,2020 Kyle J. McKay.
+** Copyright (C) 2017,2018,2019,2020,2021 Kyle J. McKay.
 ** All rights reserved.
 **
 ** Redistribution and use in source and binary forms, with or without
@@ -4590,7 +4590,7 @@ Z<> See the F<README> file for detailed release notes for this version.
 
 =item Copyright (C) 2003-2004 John Gruber
 
-=item Copyright (C) 2015-2020 Kyle J. McKay
+=item Copyright (C) 2015-2021 Kyle J. McKay
 
 =item All rights reserved.
 

README

@@ -493,7 +493,7 @@ Copyright and License
 ---------------------
 
 Copyright (C) 2003-2004 John Gruber  
-Copyright (C) 2015-2020 Kyle J. McKay  
+Copyright (C) 2015-2021 Kyle J. McKay  
 All rights reserved.
 
 Redistribution and use in source and binary forms, with or without