#!/usr/bin/perl -wl
use strict;
use HTML::Entities;
use Text::Unidecode;

my $text = "advice to Gwenda to “let sleeping murder lie.”
+";

print unidecode( decode_entities($text) );   # advice to Gwenda to "le
+t sleeping murder lie."
[download]

(i.e., decode_entities() returns a Unicode string, which you then pass to unidecode() to transliterate to ASCII)

Alternatively, with home-brewn decoding (--> chr is the function you were looking for):

#!/usr/bin/perl -wl
use strict;
use Text::Unidecode;

my $text = "advice to Gwenda to “let sleeping murder lie.”
+";

$text =~ s/&#(\d+);/chr $1/ge;

print unidecode($text);                      # advice to Gwenda to "le
+t sleeping murder lie."
[download]