Add Perl::Critic configuration

[mjgardner]

Perl::Critic tests were failing against my default (brutal, lots of policies from CPAN) configuration, so I added a bare-bones configuration file that passes. It also reports the policy modules that cause failures.

[robinsmidsrod]

@mjgardner There is already a perlcritic.rc at the root of the repo, so I don't quite understand why you need to add one in the xt/ directory.

I also can't quite see what would cause the policy ValuesAndExpressions::ProhibitAccessOfPrivateData to throw test errors. Could you please elaborate, if you can still recall why?