tac: don't print version number in usage string

* If I type a bad option I want to see the correct options, not the program version
* As done in other scripts using getopts(), support --version option by adding a VERSION_MESSAGE() function

Author: mknos

bin/tac

@@ -60,8 +60,12 @@ print while <$fh>;
 exit EX_FAILURE if $fh->get_error;
 exit EX_SUCCESS;
 
-sub usage {
+sub VERSION_MESSAGE {
     warn "$Program version $VERSION\n";
+    exit 0;
+}
+
+sub usage {
     warn "usage: $Program [-Bbr] [-s separator] [-S bytes] [file...]\n";
     exit EX_FAILURE;
 }