feat: add explicit UTF-8 handling

m2h.pl

@@ -2,6 +2,7 @@
 use strict;
 use Getopt::Long;
 use MarkdownParser;
+use open qw(:std :encoding(UTF-8));
 
 sub show_help {
     print <<"EOF";
@@ -30,6 +31,7 @@ sub read_input {
     if ($file) {
         open my $fh, '<', $file
           or die "Error: Cannot open file: $file\n";
+        binmode $fh, ':encoding(UTF-8)';
         my $content = <$fh>;
         close $fh;
         return $content;
@@ -52,12 +54,16 @@ show_version() if $version;
 
 my $input_file = shift @ARGV;
 
+binmode STDIN,  ':encoding(UTF-8)';
+binmode STDOUT, ':encoding(UTF-8)';
+
 my $input = read_input($input_file);
 
 my $output;
 if ($output_file) {
     open $output, '>', $output_file
       or die "Error: Cannot write to file: $output_file\n";
+    binmode $output, ':encoding(UTF-8)';
 }
 else {
     $output = \*STDOUT;