Start adding real HTNL report generation
Simplistic solution for removing code after __DATA__/__END__

There is no way to do it accurately without a Perl tokenizer; it should at
least double-check that it's not stripping lines covered by samples.
Add caller/callee information to report

At call sites, provide information about called subroutines, with a link
to the subroutine definition, an the subroutine header, provide links to
call sites.
Ignore missing files for now (to avoid errors for eval "" source code)