Update URL to https://tuxpaint.org/ everywhere

Also, add other social media accounts to list of places to
announce Tux Paint in RELEASE docs.

Also, list a ton more options missing from default example config file
"src/tuxpaint.conf"

src/get_fname.c

@@ -1,8 +1,8 @@
 /*
   get_fname.c
 
-  Copyright (c) 2009 - 2021
-  http://www.tuxpaint.org/
+  Copyright (c) 2009 - 2022
+  https://tuxpaint.org/
 
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
@@ -19,6 +19,8 @@
   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
   (See COPYING.txt)
 
+  Last updated: December 11, 2022
+
   $Id$
 */