avoid dependency on Carp

Carp’s output was different up to 1.24, so tests fail on old perls. I do
not wish to condone this upstream change by changing my tests, much less
condone it at the expense of users by depending on a newer Carp, which
leaves me to in-house the tiny fraction of functionality from Carp that
I actually need. Thanks to the Carp maintainer for his service.

Changes

@@ -1,5 +1,7 @@
 Revision history for Bencode
 
+	- No test failures under Carp < 1.25
+
 1.500 Wed 27 Sep 2017
 	- New $undef_mode parameter to properly handle undefs during encoding
 

cpanfile

@@ -1,7 +1,6 @@
 requires 'perl', '5.006';
 requires 'strict';
 requires 'warnings';
-requires 'Carp';
 requires 'Exporter::Tidy';
 
 on test => sub {

lib/Bencode.pm

@@ -6,11 +6,17 @@ package Bencode;
 
 # ABSTRACT: BitTorrent serialisation format
 
-use Carp;
 use Exporter::Tidy all => [qw( bencode bdecode )];
 
 our ( $DEBUG, $do_lenient_decode, $max_depth, $undef_encoding );
 
+sub croak {
+	my ( @c, $i );
+	1 while ( @c = caller $i++ ) and $c[0] eq __PACKAGE__;
+	@c or @c = caller;
+	die @_, " at $c[1] line $c[2].\n";
+}
+
 sub _msg { sprintf "@_", pos() || 0 }
 
 sub _bdecode_string {