I'm not sure if it does what you mean, but shouldn't the following do what you need?

use HTML::Entities;

my $ascii = <<'ASCII';
The quick brown fox
jumps over the lazy god.
ASCII;

my $html = encode_entities($ascii);
$html =~ s/\r?\n/<br>/g;

print "<pre>$html</pre>";
[download]

I'm unaware of any module doing that in its entirety, but maybe you want to just serve up the ascii page with Content-Type: text/plain instead of Content-Type: text/html ?